The effects of potassium fertilization and night temperatures on the absorption, translocation and assimilation of iron ...


Material Information

The effects of potassium fertilization and night temperatures on the absorption, translocation and assimilation of iron in centipedegrass (Eremochloa ophuiroides)
Physical Description:
xiii, 203 leaves : ill. ; 28 cm.
Teng, Jon I., 1930-
Publication Date:


Subjects / Keywords:
Plant physiology   ( lcsh )
Plants -- Assimilation   ( lcsh )
Grasses   ( lcsh )
bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )


Thesis (Ph. D.)--University of Florida, 1965.
Includes bibliographical references (leaves 188-202).
Statement of Responsibility:
by Jon I. Teng.
General Note:
General Note:

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Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 000469299
notis - ACN4017
oclc - 37450813
System ID:

Full Text





August, 1965


The author wishes to express his sincere appre-

ciation to Dr. W. L. Pritchett, Chairman of his Super-

visory Committee, for his suggestions during these

investigations, and for his guidance and constructive

criticisms of the manuscript. Appreciation is also

expressed to Dr. D. S. Anthony, Dr. G. C. Horn, Dr.

F. B. Smith, Dr. D. O. Spinks and especially to Dr.

T. L. Yuan for their constructive criticisms of the


The author wishes to extend his appreciation

to Dr. F. B. Smith, former Head of the Department of

Soils, who awarded the assistantship, and to the Ameri-

can Potash Institute, whose research grant helped finance

the study.

Thanks are also extended to Dr. H. H. Luke

and Mr. Clarence Selin for their assistance in the

laboratory phase.

The writer wishes to thank his wife for her

patience and understanding throughout the study.



ACKNOWLEDG*ENTS ............................... 11

LIST OF TABLES ...... ............... ...... ..... v

LIST OF FIGURES ................... ....... ... xii

INTRODUCTION ......... ......................... 1

REVIEW OF LITERATURE ......................... 4

Iron in the Soil .......... ... ........... 4

Absorption of Iron by Roots ............... 11

Properties of roots ................... 11

Factors affecting iron absorption ....... 15

Translocation of Iron in the Plant ......... 20

Mechanisms of translocation ............ 20

Factors affecting the translocation
of iron in plants ............... ...... 26

Assimilation of Iron in Plants ............. 30

Concepts of iron assimilations in
plants................................... 30

Factors affecting assimilation of iron
in plants ............................... 37

MATERIALS AND METHODS .............. ........... 42

Greenhouse-Cold Chamber Experiments ....... 42

Experiment 1 ..................... ...... 42

Experiment 2 ......... .. ................ 45



Experiments 3, 4 .nd 5 .................. 46

Laboratory Analyses ........... ........ 48

RESULTS AND DISCUSSION ...................... 55

Experiment 1 ............... ............. 55

Experiment 2 ................ ............... 59

Experiments 3, 4 and 5 ..................... 67

Plant growth ............................ 67

Plant inorganic constituents ............ 78

Some organic compounds in plants ........ 93

Some properties of centipedegrass roots 114

Soil mineral nutrients .................. 117

General Discussion ......................... 124

SUMMARY AND CONCLUSIONS ....................... 136

APPENDIX ...................................... 140

BIBLIOGRAPHY .................................. 188

BIOGRAPHICAL SKETCH ........................... 203


Table Page

1. Some physical and chemical properties
of Arredondo loamy fine sand................ 44

2. The composition of Hoagland nutrient
solutions with and without potassium ....... 46

3. Aversae maximum and minimum greenhouse
temperatures................ ........ 48

4. Analyses of variance of the effects of
treatments on the yields and inorganic
constituents in centipedegrass of
experiments 4 and 5 ...........* ........... 74

5. Effects of night temperatures, seasons of
the year, and rates of potassium and iron
applications on the iron content in centi-
pedegrass of experiments 4 and 5 ........... 81

6. Effects of night temperatures, seasons of
the year, and rates of potassium and iron
applications on the potassium content in
centipedegrass of experiments 4 and 5 ...... 86

7. Effects of night temperatures, seasons of
the year, and rates of potassium and iron
applications on the calcium content in
centipedegrass of experiments 4 and 5 ...... 89

8. Effects of night temperatures, seasons of
the year, and rates of potassium and iron
applications on the magnessium content in
centipedegrass of experiments 4 and 5 ...*** 91

9. Effects of night temperatures, seasons of
the year, and rates of potassium and iron
applications on the phosphorus content in
centipedegrass of experiments 4 and 5 ...... 92

10. Effects of night temperatures and rates
of potassium and iron applications on
the nitrogen content in centipedegrass
of experiments 4 and 5 ....... ............ 94

11. Organic acids found in leaves, stolons
and roots, in percentage of fresh weight
of plant material ........................ 97

12. Analysis of variance of the effects of
treatments on the organic acid content of
the whole plant and leaves of centipede-
grass of experiments 4 and 5 ............... 100

13a. Oxalic, citric, and malic acids in leaves,
stolons, and roots of centipedegrass of
experiments 4 and 5 ....................... 102

13b. Oxalic, citric, malic, tartaric, aconitic,
and succinic acids in leaves of centipede-
grass of experiments 4 and 5 ............... 103

14. Effects of night temperatures, rates of
potassium, and rates of iron on the total
organic contents of the leaves, stolons,
roots, and entire plants of centipede-
grass ......1.. ..... ...... ................ 105

15. Organic acids contained in leaves of
centipedegrass supplied with and with-
out iron chelate at the lowest night
temperature (-1.1 C.) ..................... 106

16. Analysis of variance of effects of treat-
ments on the amino acid content of
centipedegrass .............. ..... ...... 110

17. Analysis of variance of the effects of
treatments on the sugar content of
centipedegrass ............................. 115

18. Analysis of variance of the effects of
treatments on the extractable iron,
potassium, magnesium, calcium and
phosphorus contents of soils ............... 119

19. Available nutrients in the soil ............ 120



20. Effects of night temperatures and
sources and rates of potassium on yield
(gm. oven-dry wt.) of centipedegrass
of experiment 1 ...................... 141

21. Effects of night temperatures and
sources and rates of potassium on
iron concentration (ppm) in
centipedegrass of experiment 1 .......... 142

22. Effects of night temperatures and
sources and rates of potassium on per-
cent potassium in centipedegrass of
experiment 1 ........................... 143

23. Effects of night temperatures and
rates of potassium on yield (gm. oven-dry
wt.) of centipedegrass of experiment 2 .. 144

24. Effects of night temperatures and rates
of potassium on iron concentration
(count per minute from Fe59) in centi-
pedegrass of experiment 2 ............... 145

25. Effects of night temperatures and rates
of potassium on percent potassium in
centipedegrass of experiment 2 .......... 146

26. Analysis of variance of the effects of
treatments on iron and potassium contents
in centipedegrass of experiment 2 ....... 147

27. Effects of night temperatures, seasons
of the year, rates of potassium and iron
applications on leaves, stolons, roots
and entire plants yields (gm. oven-dry wt.)
of centipedegrass of experiments 3, 4
and 5 ............. ..... ....... .....* .. 148

28. Effects of night temperatures, seasons of
the year, rates of potassium and iron
applications on leaves, stolons, roots and
entire plants iron content (ppm) in centi-
pedegrass of experiments 4 and 5 ........ 151




29. Effects of night temperatures, seasons
of the year, rates of potassium and
iron applications on leaves, stolons,
roots and entire plants percent
potassium content in centipedegrass
of experiments 4 and 5 ................... 154

30. Effects of night temperatures, seasons
of the year, rates of potassium and
iron applications on leaf, stolon, root
and entire plant percent calcium content
in centipedegrass of experiments 4 and 5 .. 157

31. Effects of night temperatures, seasons
of the year, rates of potassium and
iron applications on leaf, stolon, root
and entire plant percent magnesium
content in centipedegrass of experiments
4 and 5 ................................ 160

32. Effects of night temperatures, seasons
of the year, rates of potassium and
iron applications on leaves, stolons,
roots and entire plants percent
phosphorus content in centipedegrass
of experiments 4 and 5 i.................. 163

33. Effects of night temperatures, rates
of potassium and iron applications on
percent nitrogen content of leaves,
stolons and roots of centipedegrass
of experiment 5 ......... ...... ......... 166

34. Effects of night temperatures, rates of
potassium and iron applications on
percent oxalic acid content of leaves
of centipedegrass of experiments 4 and 5 .. 167

35. Effects of night temperatures, rates of
potassium and iron applications-on
percent oxalic acid content of leaves,
stolons and roots of centipedegrass of
experiment 5 ......*.......**......... ..... 168




36. Effects of night temperatures, seasons of
the year, rates of potassium and iron
applications on leaves percent oxalic acid
content in centipedegrass of experiments
4 and 5 ............ .......... ............. 169

37. Effects of night temperatures, rates of
potassium and iron applications on leaves
stolons and roots percent citric acid
content in centipedeprass of experiment 5.. 170

38. Effects of night temperatures, seasons
of the year, rates of potassium and iron
applications on leaves percent citric
acid content in centipederrass of
experiments 4 and 5 .................... 171

39. Effects of night temperatures, rates of
potassium and iron applications on leaves,
stolons, roots percent malic acid content
in centipedegrass of experiment 5 ......... 172

40. Effects of night temperatures, seasons
of the year, rates of potassium and
iron applications on leaves malic acid
content in centipedegrass of experiments
4 and 5 ................... ............. 173

41. Effects of night temperatures, seasons
of the year, rates of potassium and
iron applications on leaves percent
tartaric acid content in centipedegrass
of experiments 4 and 5 .................... 174

42. Effects of night temperatures, seasons
of the year, rates of potassium and
iron applications on leaves percent
aconitic acid content in centipede-
grass of experiments 4 and 5 ................ 175

43. Effects of night temperatures, rates
of potassium and iron applications on
leaves percent succinic acid content
in centipedegrass of experiment 5 ......... 176



44. Effects of night temperatures, rates
of potassium and iron applications on
leaves, stolons, and roots percent
aspartic acid in centipedegrass of
experiment 5 .......................... .. 177

45. Effects of night temperatures, rates
of potassium and iron applications on
leaves, stolons and roots percent
glutamic acid in centipedegrass of
experiment 5 .... ..... ................. 178

46. Effects of night temperatures, rates
of potassium and iron applications on
leaves, stolons and roots percent
glycine in centipedegrass of
experiment 5 ........ .... .. .............. 179

47. Effects of night temperatures, rates
of potassium and iron applications on
leaves, stolons and roots percent
histidine in centipedegrass of
experiment 5 ............. ............ .... 180

48. Effects of night temperatures, rates
of potassium and iron applications on
leaves, stolons and roots percent
isolencine content in centipedegrass
of experiment 5 ........... ........... ..... 181

49. Effects of night temperatures, rates
of potassium and iron applications on
leaves, stolons and roots percent
reducing sugar content in centipedegrass
of experiment 5 ........................... 182

50. Effects of night temperatures, rates
of potassium and iron applications on
leaves, stolons and roots percent
cold water extractable carbohydrate
in centipedegrass at experiment 5 ......... 183

51. Effects of night temperatures, rates
of potassium and iron applications on
the reductive capacity of root in centi-
pedegrass of experiment 5 ...*.........**.. 184



52. Effects of night temperatures, rates
of potassium and iron applications
on cation exchange capacity of roots
in centipedegrass of experiment 5 ........ 185

53. Chemical analyses of Arredondo loamy
fine sand at the conclusion of
experiments 4 and 5 ...................... 186

54. Soil nitrate (ppm) determined at
the conclusion of experiment 5 ........... 187





Figure Page

1. The effect of night temperatures and
potassium sources on the concentration
and total absorption of Fe and K in
centipedegrass ......... .............. ........*.... 56

2. Iron and potassium in centipedegrass
as affected by three rates and two
sources of potassium........ ,.....................58

3. Effects of night temperatures and rates
of potassium on yields on centipedegrass..........61

4. Effects of night temperatures and rates
of potassium on concentration and
total absorption of iron in centipedegrass........63

5. Total iron (Fe59) and potassium contained
in tops and roots of centipedegrass
at three growth periods...........................65
6. Effects of night temperatures and rates
of potassium in the presence of added
iron on the appearance of centipedegrass..........68

7. Effects of night temperatures and rates
of potassium in the absence of added iron
on the appearance of centipedegrass...............69
8. Effect of night temperatures, rate of
potassium and iron on leaves of centi-
pedegrass...............................*** ******* 71

9. Effects of night temperatures, rates of
potassium and iron on roots of centi-
pedegrass.. e o.......... **.***.**'*****************72

10. Effects of night temperatures and seasons
on yields of centipedegrass.............********** 77

11. Effect of night temperature and rates of
iron on the root yields of centipedegrass.........79


12. Effects of rates of potassium on yields
of centipedegrass.... .. *.... ....................79

13. Effects of night temperatures and rates
of iron on the iron content of leaves,
stolons, roots, and entire plants of

14. Effects of rates of potassium and night
temperatures on the percent pot-ssium
in leaves of centipedpgrass.... ..................87

15. Paper chromato-rnm of organic acids from
leaves, stolons, and roots of centipede-
16. Paper chromatogram of amino acids from
leaves, stolons, and roots of centipedegrass.....108

17. Effects of night temperatures on the percent
of aspartic and glutamic acid in leaves,
stolons and roots of centipedegrass..............111

18. Effects of night temperatures on the
percent of glycine and isolencine in
leaves, stolons and roots of centipedegrass......112

19. Effects of night temperatures on the
percent of histidine in leaves, stolons
and roots of centipedegrass.............*........113

20. Effects of night temperatures on reductive
capacities of roots of centipedegrass............116



In a modern, highly mechanized society, turf-

grasses play an increasingly significant role by adding

beauty to mundane environments and serving as foundations

for play areas on which man can spend his leisure time.

Grasses are the principal ingredient in landscaping

for homes and public buildings and in golf courses,

parks and playgrounds. Several varieties of turfgrasses

are used for this purpose in Florida. Among these,

centipedegrass has been one of the most popular since

about 1920 due to the low maintenance requirements.

However, there has been a gradual decline in the popu-

larity of centipedegrass during the past decade due, in

part, to the yellowish, chlorotic appearance often

found in spring and early summer. Bryan reported in

1933 (32), that this unattractive discoloration could

be ameliorated by intermittent spray of the chlorotic

grass with an iron sulfate solution. Consequently,

this yellowing of centipedegrass has been referred to

as "iron chlorosis."

Centipedegrass grown in plots at the University

of Florida Horticultural Unit, on Arredondo loamy fine

sand, often exhibited a chlorotic appearance from early

spring to early summer when the night temperatures were

relatively low. This chlorosis has been reported (72)

to be closely related to applications of high rates of

potassium fertilizers and to be more prevalent during

periods of rapid growth, particularly where high levels

of nitrogen were also applied (73). Among the soil

factors often mentioned as being associated with soil

iron availability are (a) a high content of phosphates,

(b) a pH of 6.5 or above, (c) the presence of large

amounts of bicarbonates, (d) an excess in heavy metals,

(e) competition from soil microorganisms, and (f) a high

oxidation-reduction potential of the soil. It is also

believed that a chlorotic condition in plants may be

induced by the physiological failure concerning the

uptake of an adequate amount of iron, or the difficulty

in the assimilation of iron by the plant. The chlorosis

in centipedegrass associated with low night temperatures

and/or high rates of potassium fertilizers may result

from either a deficiency in available soil iron or with

an inhibition in the absorption, translocation or

assimilation of iron by the plant--or a combination of

these factors.

This research was undertaken to study the effects

of certain night temperatures and rates of potassium

fertilizers on the absorption, translocation, and


assimilation of iron and on the organic and inorganic

composition of centipedegrass, and to attempt to relate

these properties of the plant to the prevalence of

"iron chlorosis."


Iron in the Soil

Iron, the fourth most abundant element in the

earth's crust, composes 6 to 7 percent of the soil

mass and is found mostly as oxides (79). Iron occurs

in primary minerals as ferromagnesian silicates. The

iron-bearing secondary minerals are biotite micas, and

the commonly occurring free iron groups are iron oxides

and inorganic and organic iron salts (111). Iron oxides

are the compounds that hold the greatest interest for

agriculturists. Iron oxides include (a) hematite,

Fe203, red in colors (b) goethite, Fe203 nH20, brown

or yellow; (c) matite, Fe203, a dark iron compound; and

(d) magnetite, Fe304, a mixture of ferric and ferrous

iron (111). Inorganic iron salts are compounds of

hydroxides, carbonates and sulfates. Organic iron salts

occur in soil organic colloids (71, 119).

Soil scientists are interested in free iron

oxides in soil because they are involved in a great many

soil problems. For example, poor drainage and other

farming difficulties are often associated with the

problems of iron concretions. Furthermore, the availa-

bility of phosphorus due to iron fixation at low soil

pH, or adsorption of phosphates on the surface of the

iron oxides at high soil pH (111) is often a problem

in soils high in iron. On the other hand, of significant

importance is the nutritional value of iron to a green

plant in the formation of chlorophylls (17, 38, 99).

Although the total amount of iron in soils is

generally high, there often is a deficiency of available

iron due to the stability of the ferric oxidation form,

Fe3+ (49, 54, 79). Thus, to understand iron nutrition,

it is necessary from the very beginning to study the

transformation processes of soil iron under different


The majority of iron in agricultural soils is

present in an insoluble form as Fe3+, which is the

stable oxidation state. The lower oxidation state of

Fe2+ usually occurs in soils in quite small quantities.

However, it is the ferrous iron, Fe2+ which has been

reported (49, 119) as the form plant roots can most

readily absorb, since ferrous salts have relatively

higher solubility product values. The solubility product

values of Fe(OH)2, FeC03, and FeS04 are 1.6 x 10-14 at

pH 8.0, 3.5 x 10-11 at pH 7.0, and 3.7 x 10-16 at pH

7.0, respectively (119). In contrast, Fe(OH)3 has a

very low value, 6.0 x 10-38, at pH 4.0 (148). Further-

more, ferrous iron fulfills a greater number of physio-

lo,.dical functions than ferric iron inside the plant

(113, 116, 146, 149).

Both ferrous and ferric iron in soils are capable

of movement in the form of organic complexes if sufficient

amounts of low molecular weight orranlc acids are

replenished by the decomposition of organic matter (49).

Polyphenols, such as catching, which can be released from

fresh organic matter, are the other agents utilized in

translocating iron compounds (111). Nevertheless, iron

movement may be stopped if the soil undergoes alkaline

reactions which result in low iron solubility, or if

there is a sufficient concentration of transition elements

present which tend to replace the iron from the organic

complex (111).

The stability of an organic iron complex depends

on the nature of its anion component (49). The order of

these organic anions on the basis of their strength in

forming organic complexes is:

citrate > oxalate > tartrate > acetate

The order for the inorganic anions is:

hydroxyl > arsenate > borate >'thiocyanite>

sulfate r chloride nitrate

Chemically, ferrous iron is generally predominant

in soils with pH below 5.0, while above pH 6.0 ferric

iron will be predominant (1). Whenever a high pH

condition is built up due to alkaline end products from

soil microorganisms, or from other oxidation processes,

ferric iron will be precipitated from the soil solution.

Oxidation-reduction potential plays an important

role in determining the forms of iron In soils. There

exist a great many redox systems. The oxidation

potentials of these systems usually vary from the

equivalent of hydrogen's redox system, 0.00 V, to that

of oxygen's redox system, 1.23V. Ponnampeuma (119) has

discussed these systems in detail in his study of

submerged soil. Several of them are reviewed below:

E(V) at
Redox System Eo(v) pH 7.0

02 + 4H1+ + 4e- 2 2H20 1.23 0.82

Fe + e-

inO2 + 4H+ + 2e-

NO- + H20 + 2e-

Fumarate + 211H +

Oxalate + 2H+ +

Fe(OH)3 + 3H+ +

Fe(OH)3 + e-

2e --



A general redox system is

Oxidant + ne- _


Mn2+ + 2H20

N02- +. 20H"



Fe2+ + 31120

Fe(OH)2 + OH"









-0.13 1

-0.14 2

of the following nature:


1At pH 6.5, calculated by the author.
2At pH 7.0, calculated by the author.

Then, the Nernst equation is used to calculate the

oxidation potential:
RT Oxidant
E = Eo + n
S f Reductant

In this equation, where E is the oxidation

potential, R is the gas constant, T is the absolute

temperature, n is the number of electrons lost in the

change from reduced form to oxidized form, f is the

value of Faraday and Eo is the standard oxidation

potential (20). When the concentration of oxidant and

reductant has unit ratio, the oxidation potential E is

equal to the standard oxidation potential Eo (20, 38).

In the above list of redox systems any one

system will be able to oxidize the one below it. Since

the oxygen system has higher Eo (1.23V+) in the soil,

this system can oxidize the rest of the systems which

appear in the list. A well-aerated soil, therefore,

may have deficiencies of some nutrients due to this

oxidation of soluble reduced forms of the nutrients to

insoluble oxidized forms. The majority of soil pH

values fall between 5.0 and 9.0 (1, 69), therefore a

redox system occurring in soils should involve the

concentration of hydrogen ions (119). A general equation

involving the hydrogen ion is:

Oxidant + mH+ ++ ne- Reductant
SRT Oxidant H+ M
Eh = E + In eductant
nf Reductant

Eh is the oxidation potential at a certain

concentration of H+. Commonly, pH 7.0 is taken as the

condition to calculate Eh. This equation clearly shows

that a change in pH will influence a system's oxidation


The standard oxidation potential of Fe3+ --- Fe2+

is 0.77v, which indicates that PFe2+ is quite stable in

an acid solution. Whenever a higher redox system, such

as that of oxygen, exists with the Fe3+ --* Fe2+ system,

a redistribution of the electrons will result in a

spontaneous reaction favoriir; the reduction of oxygen

to water (20, 119) and leaving the iron in Fe3+ form.

The same thing happens when iron reacts with a man nnese

system. Ponnampeuma (119) believed that ferric iron

could not be reduced until a considerable amount of

nanranese had been reduced, and that nitrate reduction

could start only after nearly all of the mang-nese was

in reduced form. When the soil pHI gradually approaches

neutrality the man 'nnese and nitrate systems have about

the- same reduction potential, 0.43 V and 0.41 V, respec-

tively, so that these systems are reduced simultaneously.

However, the oxidation potential of the iron system

drops drastically to -0.142V Therefore, the reduction

of iron will be very difficult because it is governed by

all the systems above it. Evidently reduction of manga-

nese and nitrate plays an important role in controlling

the iron system as soil pH increases. Manganese is one

of the transition metals which is known to induce iron

chlorosis in some tree species (29). Furthermore, soils

high in nitrates and undergoing vigorous reduction

processes have caused iron chlorosis in pineapple and

other plants (1, 18). In a soil of pH 7.0, minrranese and

nitrate systems have retarded the reduction of iron and

stabilized the potential at 0.2 V to 0.4 V (18). In

addition, the formation of or. inic complexes have a

marked effect on the oxidation potential of a redox

system by reducin:' the oxidation potential and rendering

metals to their reduced forms (46, 71). The reduced form

of iron, Fe2+, possibly functions as an exchanrgeable

cation, since the amount of Fe2+ ion extracted by a KC1

solution was much more than that extracted by an aqueous

solution (74).

Iron transformation takes place in the presence

of soil microorganisms, and the existing forms of iron

are-influenced by the type of microbes. A :roup of

bacteria, called iron bacteria, oxidizes ferrous iron to

ferric iron (1). Many heterotrophic species attack

soluble organic iron salts causing the iron to precipitate

out as ferric iron (1). Groups of bacteria can produce

acid end-products that reduce ferric iron to ferrous iron

(71). Under anaerobic conditions, a large number of

reducing agents, such as sulfides, reduce ferric to

ferrous iron (1). Anaerobic microorganisms can also

stabilize iron in the ferric state by utilizing the oxygen

of nitrate in preferenre to oxygen of iron oxides (1, 49,


Low soil temperature may affect the transformation

of iron through its immediate influence on nitrate

reduction (22). A decrease in nitrate reduction with

decreased temperature results in more available iron. A

low soil temperature and high moisture increased the

solubility of iron due to delnyed nitrate reduction in

submerged soils (119).

Absorption of Iron by Hoots

In grasses, there is a zone close behind the root

tip bounded externnlly with piliferous roots. Grasses

grown in sandy soils usually exhibit long and persistent

root hairs (49). The root hair zone has several important

properties which are responsible for the absorption of

iron and other ions.

Properties of roots

The cation exchange capacity of the root has been

extensively studied by a great many people (49, 50, 51).

Jenny (84) produced a picture of mucilaginous substance

about roots believed to be pectic material on the root

cell wall and thought to serve as cation exchange sites.

Drake (49) reported that dicotyledons usually have higher

root cation exchange capacity (CEC) than monocotyledons.

Many workers (45, 51, 84) have shown that roots high in

CEC absorbed more divalent cations than monovalent cations,

while plants with low root CEC absorb a higher percentage

of monovalent cations. An inverse relationship between

potassium and CEC and a direct relationship between

calcium and CEC has been recognized in legumes (49).

However, the inverse potassium-CEC relationship can be

found only when there exist a low concentration of

potassium and a high concentration of calcium as explained

by Wallace (45). It has been reported (49) that roots

with a high CEC has greater uptake of iron than did roots

with a low CEC. The root CEC of several grasses generally

has been found to be below 30 m.e./100 gm. dry weight,

which is lower than most dicotyledons but higher than

most cereals (49).

Brown et al. (28) have shown that non-chlorotic

Hawkeye soybeans have roots of higher reductive capacity

and higher content of reduced cytochrome c than did

chlorotic PI 54619-5-1 soybean. The reductive capacity

was expressed as the capability of roots to reduce

ferricyanide to ferrocyanide. This reductive capacity

in roots was also found (28, 49) to be influenced by

the upper portion of the plant and the ability of the

plant to synthesize various products.

(The presence of natural chelating agents has

been observed in many plants roots (26, 46, 123, 151).

For example, the chlorotic '3oyhrnn PI 54619-5-1 was found

by Brown (28) to have low root chelation capacity, while

non-chlorotic Hawkeye soybean has high ohelatlon capacity.)

The most effective natural chelating agents in the roots

are citric, tartaric, oxalic, and amino acids (49).

The specificity of a chelatin:~ agent is supposed

to have great importance, according: to Wallace (147).

That is, certain chelating compounds are specific for

absorption of sodium, masnesium, and iron; and others

are involved in the accumulation of potassium, calcium,

magnesium, and sodium in biological systems (148). This

indicates that natural chelating agents are selective

in regard to plant nutrients. In several cxrintes

collected from plant species (123), there appeared to

be-both qualitative and quantitative differences in

these natural chelating qirnths. It has been shown (123)

that iron present in the plant exudate was in a chelated

form. However, the or7Rnic component was not identified.

There are also reports of the synthetic chelating agent

entering into plant tissues with chelnted metals (26).

They may or iniy not dissociate in the course of translo-

cation, depending on the characteristics of the natural

chelatifn ngnts and upon the pTI of the plant sop (134).

Plants have a great quantity of organic acids which is

usually correlated with a highly active chelating nature.

Citric, malic, and oxalic acids have been found in the

roots of most plants (49). Ulrich (144) indicated that

the or:.-anic acids in barley roots iny be stimulated by

a high absorption of K+ in a solution of iKCO3.

Generally, small amounts of reducing sugars can

be found in root tissues. The reducing sugars D-glucose,

D-fructose, D-galactose, and D-mannose are capable of

reducing the higher oxidation state Fe3+ to the lower

oxidation state PF,2+ (28). The cold water extractable

carbohydrates which include d-malate, p-cellobiose,

and. -lactose also have reducing powers (38). The high

absorption capacity of a root is directly proportional

to its reducing su, ar content. It is reported that an

increase in soluble reducing sugars can greatly enhance

the uptake of cations (31). On the other hand, the lack

of sufficient K+ in the plant tissue lmay result in a

high amount of reducing su -irs in roots (39, 96, 134).

This may facilitate iron absorption, but at the same

time less iron would be used in metabolic activities

due to a block in carbohydrate synthesis (93).

Growth of the root increases the number of

binding sites and therefore, increases the total uptake

of nutrients. One of the essential elements in increas-

ing the growth of root is potassium (93, 105). Another

important factor affecting plant root growth is temper-

ature (37, 52, 64, 106, 107). In general, growth of

roots decreased with increases in soil temperature, as

observed in oats (22), buckwheat (62), and Kentucky

bluegrass (23). Temperature also affects the morpho-

logical characteristics as reported by various research-

ers (120, 121). With a soil temperature at 100 C. roots

were white, translucent, and relatively unbranched; at

15.60 C., roots were slender, profusely branched, and

longer; and at 26.70 C. roots were very fine and fibrous

but less extensive (121, 131). The total nbsorption of

ions by roots was often related to the vigor of root

growth which, in turn, was the function of soil temper-

ature up to a limit of approximately 400 C. (37).

Factors affecting iron absorption

Iron is absorbed by roots through three mechan-

isms according to Glauser (60). The first is CO2

pressure. The CO2 evolved from cellular respiration of

plants and soil microflora dissolves in the soil solution

as carbonic acid which brings some ferric into the soil

solution to form ferrous iron. The second Is synthesis

of chelating a ~ents. A third, surface contact, implies

root contact oych1nr'e that is related to the C:IC of the


It is assumed that plant roots can not absorb

F3+ directly. The ferric Fe3+ must first be converted

to Fe2+ (88). However, this may not hold true for all

plants. Bell et al. (8) found that one genotype of

corn, could absorb Fe3+ where another failed to absorb

Fe3+ when they were placed in the same ferric iron

solution. The r:eson for a plant failing to absorb Fe3+

might be due to its accumulation in the root tip (89)

or due to precipitation of Fe3+ on the roots' surface

(46). The accumulations of ferric iron in the root tip

were in the form of insoluble phosphates and organic

iron complexes since tips of roots have high rates of

metabolic activity but have no conducting tissue (89).

Iron precipitated on the surface of roots primarily as

ferric ph:n.-plih tes (11, 46).

The effect of potassium ion on the uptake of

iron in plant roots has been observed to be an inverse

relationship in many plants (63, 124). It was not clear

as to which factor caused the deficiency of the other.

Some workers (140, 146) in discussing high concentrations

of potassium associated with low concentrations of iron

have designated iron as the cause and potassium as the


Shear's statement (124) and the cation-

equivalent-constancy hypothesis in plants (146) indicate

that at a (.ven concentration of anions any increased

accumulation of one or more cations must be accompanied

by an equivalent decrease in one or more of the other

cations. Therefore, whenever luxury consumption of

potassium is favored, other cations suffer a depression.

For example, the uptake of calcium, mq-gnesium, and iron

decrease in the presence of a lnrrer quantity of potas-

sium (108).

The absorption of potassium was reduced by

treating the roots with CO2 (49). High concentrations

of CO2 reduced nutrient uptake by the roots in the order

of K > N > P v Ca I;:g (49). However, the uptake of

iron was relatively increased as the CO2 partial pressure

increased in the soil (66). This suf;ests a possible

cause for the inverse relationship between potassium

content and iron content in a plant.

There have been many reports (10, 16, 41, 63,

65, 95, 118, 124) on the inverse relationship between

potassium and iron in sucar cane, potato plants, pasture

grasses, and tunr trees. On the other hand, reports

showed that potassium fertilization increased the

absorption of iron by increasin; the rate at which the

inorganic phosphates were converted Into organic

phosphates (3, 145). This activated the insoluble

inorganic iron phosphates on-the root surfaces and

allowed them to move into the root cells (34). Ponnam-

poumn (34, 119) reported that the addition of potassium

caused some iron that had accumulated in the roots of

sugar cane to pass upward in the plant.

Other cations which affect the absorption of

iron appear to be zinc, calcium, manganese, and copper.

Epstein (54) states that iron absorption in some plants

was a function of the ratio of calcium to hydrogen in

the soil. In soil solutions with the ratio of calcium

concentration to that of hydro-o~ from 0.25 to 0.75,

the plant roots could take up iron without trouble.

Iron absorption decreased sharply when the ratio became

0.92. I oiinnese has been known to decrease iron content

in some plants (54, 125, 130, 140). Copper, accumulated

in Florida sandy soils, caused iron chlorosis in citrus

(71). However, it has been reported (26) that a heavy

application of copper increased ascorbic oxidase. To

counteract the increasing ascorbic oxidase activity,

the activity of the cytochrome oxidases increased, which

resulted in greater iron absorption (26).

The anions which mny possibly affect the absorp-

tion of iron are bicarbonates, phosphntes, nitrates,

and chlorides. Usually, the first two anions affect

iron absorption to a greater extent than the latter two

anions. Bicarbonates reportedly reduced the iron contents

of some plant tissues (7, 25, 27, 29). As reported by

Holmes et al. (71), irrigation c-iused chlorosis of

peach trees, and the decomposition of or-qnic matter

intensified chlorosis of other fruit trees. The chlorosis

was due to the high concentrations of bicarbonates pro-

drced in the processes. Bicarbonate effects iron

absorption through increase in the soil pH and the

solubility of phosphates (9), which decreases iron

solubility in the soil solution (29). That phosphates

will precipitate iron out of soil solution and deposit

it on the surfaces of roots is rather well established

(2, 48). Nitrate reduction, which takes place in root

tips, will decrease the availability of iron (1, 71).

The effect of chloride ions on iron absorption is less

understood (71). The rate at which chloride is absorbed

by the roots is about the same as the rate for nitrate

ions (144).

Lundegardh (97) stated that the absorption of

anion is a much more temperature-dependent process than

-the absorption of cations. He calculated the temperature

coefficient, Qio0 for the absorption of nitrate as

2.0 2.5 and Q10 for potassium as 1.4. Q10 is defined

as: the ratio of reaction rates at two temperatures

100 C. apart (99). The equation given by Wallace and

Sufi (147) is
(T2 T1)/10
Q10 uptake of T 2
uptake of T1

where Tj and T2 are temperatures in o C. A value of

Q10 less than 1.5 is regarded as a physical phenomenon
and larger than 2.0 as a chemical process (99).

A rising in soil temperature did increase the

activity of bicarbonate ions (25, 71) which rendered

iron deficiency. Soil iron availability had been

decreased by lowering the pH of soil solution due to

low temperature (83). Saric et al. (122) studied the

relationship between soil temperature and iron absorption

in wheat. They found that the iron content of leaves

was greater at temperatures of from 40 to 300 C. while

plants grown at temperatures on either side of this

range had lower iron content.

Translocation of Iron in the Plant

Mechanisms of translocation

Ions in soil (5) taken up by roots either

accumulate in the vaouoles or move in the cytoplasm.

host probably the ions that enter the xylem to be

translocated to the top tissues are the ones found in

the cytoplasm. A scheme for translocation of ions in

plants as described by Fried and Shapiro (58) is:

g ^k2
M + R -.- MR ;-f M(accumulated in roots) + R1
k1 j -k?
7 Transpiration
M(xylem) M(in shoots)

M represents the ions in soil solution, R is the carrier

at the binding site in plant roots, k2 is the rate of

turnover of ion, and k1 is the rate at which ion is

translocated. Minerals or ions taken up by carriers on

the protoplasmic membrane form complexes of MR. MR mny

deposit M in the vacuole or M can be released from the

complex and enter into the xylem. The minerals or ions

appearing in the xylem are carried up along the transpir-

ation stream to the top of the plant. The rate of

transpiration is slow during the night and rapid during

the day, while the rate of root respiration is the

opposite. nevertheless, the energy for translocatin,

minerals is produced by the mechanism of respiration

(43, 91, 112, 138). The translontied minerals or ions

may have four different destinations varyiT-r with plant

tissues, individual minerals, and immediate metabolic

conditions (11). The destinations are: (a) acceptance

by cells adjacent to xylem, (b) lateral movement via

rays to the actively metaboli7zno cells, (c) depositions

in leaves, and (d) to the apical primordia. Minerals

accumulated in small vacuoles would possibly be trans-

ported, except for those in the xylem, through the

plasmodesmata in the sieve tubes of the phloem. The

vacuole translocation through plasmodesmata is usually

conducted in darkness (134, 135).

Iron translocation in plants was shown by Brown

et al. (21) through an application of Fe59 to a plant

leaf. This iron isotope was translocated throughout

the phloem to the newly formed leaves and to the tips

of roots. This translocation of iron is equally

effective when it is applied to roots (148).

The idea that the rate of nutrient translocation

is directly proportional to the rate of transpiration

probably does not hold, according to Sutcliff's review

(134), since an increase in the osmotic pressure of the

external solution decreased transpiration but did not

affect mineral absorption. Therefore, the translocation

of minerals probably is in chelated form with organic

compounds. There were a great number of researchers

(12, 15, 56, 57, 82, 101, 136, 137) who had called

attention to the consideration of the translocation of

these organic compounds in the plants.

All organic compounds, such as the photosynthate,

the metabolic intermediates, and other assimilates are

translocated through the phloem to all non-synthesizing,

but synthates requiring sites in the entire plants (6, 12,

15, 66). An interesting observation on the translocation

of the organic compounds in the plant (89) is that when

an organic compound is translocated from a green portion

of a leaf to a colorless part of the same leaf, it first

flows down the phloem to the roots and then rises again

through the xylem to the colorless portion.

The destination for organic compounds from a

green leaf depends on the leaf position (11). The lower

leaves send organic compounds to roots; the uppermost

leaves send them to the apex; while the intermediate

leaves send them in both directions, all via the phloem.

The rate of flow of organic compounds toward the roots

is greater during the vegetative growth period because

the roots need these compounds to maintain a high

activity of absorption (141).

Sucrose is believed to be the first synthate

sent into roots (136). It was found that glucose and

fructose compose only 3-10 percent of the total sugars

sent to roots of sugar beets (144). But reducing sugar

was the primary form found in the phloem of the guayule

tree (39, 40). Temperature has great influence on sugar

transportation. The Q10 for sugar translocation in

tomato (153), in Bilox bean (89), and in sugar cane (152)

was usually less than one. This led Went (152) to

hypothesize that translocation of sugar from leaves to

the other parts of the plant is faster at low tempera-

tures. Went and Hall (153) found that in some plants

localized sugar movement could be brought about to a stop

at temperatures of 20 to 50 C., but to stop the plant's

entire sugar movement the temperature should be 0 to 20C.

Most of the organic acids seem to accumulate in

surrounding cells of the phloem rather than entering into

the flow path and therefore, are only weakly exported

from assimilating sites of the leaves (89). However,

citric and malic acids are exceptional in that they are

transported in a considerable amount (89, 100, 144).

Nevertheless, sugar in the phloem can be converted into

very small amounts of organic acids. Ulrich (144)

showed that temperature was negatively correlated with

the amount of total organic acids in the excised barley

roots. In another experiment Ulrich (144) and others

(59, 61) showed that a positive correlation existed
between total organic acids and total cations absorption.

Kursanov (89), reported that amino acids comprise 0.2 to

12 percent and in some cases up to50 percent of the total

translocated assimilates. The rate of movement of amino acids

was estimated to be between 370-1,390 cm./hr. in 20-24

day-old soybeans. ielson ot al. (106) observed, that

glutamic acid and glycine moved slowly in the soybeans

and that alanine, serine, and aspartic acid moved

rapidly. Amino acids, like sv'-r, can be translocated

from leaves to roots via phloem and also from roots to

leaves via the xylem. Low temperature delays the trans-

portation of amino acids from leaves to roots (137).

Brown (22) reported that when the shoots and roots of

Bermuda grass were held at 100 C. and those of orchard

grass, Kentucky bluc rass, and Canada bluegrass held at

4.40 C., translocation of nitro:-en assimilates wasretarJed.

He attributed this retardation to the slow synthesis of

nitrogen containing assimilates. Furthermore, tempera-

ture affected the types of amino acids found in the

obinia p1seudocaacia (89). Durin: summer primarily

glutamic acid, leucine, and valine were found in the

phloem; during autumn, proline replaced glutamic acid

and the others remained the same. The concentration of

amino acids is usually higher in autumn than in summer

(22, 89).

The effect of alternate day and night tempern-

tures on the translocation of or-gnic compounds in the

conducting tissues has received considerable study.

Nelson et al. (106) and Thrower (141) realized that the

process of translocation in a plant was much easier in

the night than in the daytime. Kursanov (89) reviewed

that organic compounds in the pumpkin plant were trans-

ported almost exclusively at night. The lower night

temperatures appeared to affect the translocation of

organic compounds from leaves to root of sugar beets

much more than higher night temperature, as pointed out

by Ulrich (144). He found that beet root had sugar con-

centrations of 11.9 percent at a night temperature of 20

C. and only 7.2 percent at a night temperature of 300 C.

The sap of conducting tissue is rich in K-con-

taining compounds, approximately 2 percent of potassium

was found in the phloem sap of Salix viminalis, according

to Kursanov (89). However, he reported only low percent-

ages of calcium and sodium in the sap. He explained the

high concentration of potassium in phloem sap as due to

potassium containing enzymes, such as phosphofructokinase,

pyruvatekinase, and aminopherase.

Factors affecting the translocation of iron in plants

During the translocation of iron from roots to stem

a change in the supply of oxygen partial pressure to the

root will cause a change of speed in translocation. DeKock

(46, 47) recorded that plants grown in an atmosphere of 1

percent oxygen contained much more iron in the stem than

those with 20 percent supply of oxygen. The author did

not explain whether the low iron in the stems of the

latter was a result of an oxidation state change from

Fe2+ to Fe3.

Temperature may either accelerate or slow down

the translocation of nutrients (98, 128). The tempera-

ture coefficient, Q10, is a means to determine whether

a given ion is transported or metabolically accumulated.

Cool temperatures inactivated iron although it did not

prevent iron absorption by plant roots (140). Branton

and Jacobson (19) reported that the movement of iron in

peas depended on metabolic energy. The metabolic energy

is derived from cellular respiration and respiration is

influenced by temperature (43, 44, 128).

The translocation of potassium in plants is a

temperature-dependent phenomenon (107, 108, 117).

Hoagland and Broyer (68) reported that the Q10 for

potassium translocation was 3.0 at 0.5 to 2.00 C. Hartt

(63) reported that iron was found accumulated in the

root and stem in iron deficient sugar cane. The

addition of potassium to the soil caused some of the

accumulated iron to pass into the leaf blade. Ponnampeuma

(119) reviewed that the accumulation of the iron in the

nodes of corn plants was cleared up when heavy applica-

tions of potassium were made. A close association has

been observed between iron toxicity and potassium

deficiency in rice, corn, sugar cane, and other members

of the Gramineae (63, 87, 137). Poninampcuma (119)

commented on the relationship of potassium to iron

translocation: "The ameliorative effect of potassium

to which numerous investigators have drawn attention may

be ascribed to the peculiar ability of potassium to

mobilize the deposit of iron in the tissue."

Biddulph (11), who studied Fe55 distribution,

showed that the translocation of iron was controlled by

the prevailing status of pH and phosphorus. He indicated,

first, that iron rapidly entered into and was distributed

equally throughout the vein-mesophyll at a piH of 4.0

with medium phosphorus. Secondly, iron rapidly entered

into the vein but with little or no distribution in the

mesophyll at pH 7.0 with medium phosphorus. Thirdly,

iron failed to enter the xylem and precipitated at the

root surface at pH 7.0 with high phosphorus. This

clearly shows the influence of the hydlro;jen ion and

phosphorus concentrations in the substrate on the dis-

tribution and translocation of the iron. An experiment

with Fe59 conducted on bush bean by Wallace (146) showed

that the plant at pH 8.0, had a decrease in translocation

of the iron from the vein to the mesophyll than at the

lower pH. This is in agreement with Biddulph's finding

(11). In another experiment, iron was found to have

precipitated in the conducting tissue at high pH,

clogging conducting tissue (70).

Iron is a very important element in synthesizing

several metallo-enzymes essential for biological systems.

Nevertheless, the element may be inactivated by forming

various organic salts. A ,reo.t number of organic

compounds may compete for iron; those organic compounds

may be classified in four groups (121, 129):

(a) Hydroxymonocarboxylic acids, such as lactic
acid (CH3CHOHCOOII) and gluconic acid (CH20H (CHOH)4 COOH),

(b) Dicarboxylic acids, such as oxalic (HOOCCOOH),

and malonic acid (IOOCCII2COOH),

(c) IHydrojdicarboxylic acid, such as tartaric

acid (HOOC (CHOH)2 COOH), and citric acid (HOOCCH2


(d) Amino acids, which are also hydroxy or dicar-

boxylic acids, such as glutamic acid (HOOC (CH2)2 CH(NH2)

COOH), Aspartic acid (HOOCCH2CII(NH2)COOH), and cysteine


These hydroxyl and carboxyl groups react with iron to

produce associated organic iron compounds. These

inactivated iron compounds most probably would be found

at the organic compound synthesizing sites of the leaves

(42, 94, 129).

Due to the many difficulties that iron may en-

counter during its translocation and in the metabolically

active sites, the active iron which actually participates

in metabolic work may possibly be only a small portion

of the total iron content of the plant.

A imil-ti-on of Tron in Plnnts

Concepts of iron assimilations in plants

Iron problems are usually associated with

chlorophyll formation in the plant. However, iron is

not involved in the chlorophyll molecule, but it does

function as a prosthetic group to a large number of

enzymes in catalyzing chlorophyll synthesis (36, 38,

55). Furthermore, nuicrous physiological functions are

performed by iron throur:h its enzymatic activities.

Enzymes having heme iron (iron porphyrin com-

plexes) as prosthetic groups are cytochromes, catalase,

and peroxidase. The cytochromes act as mediations in

cellular respiration (17, 38). In the electron transfer

system, cytochromes carry o:y,:;en to react with the hydro-

gen ion to form water and gives rise to ATP by oxidative

phosphorylation. The cytochrome b6 and cytochrome f

are two enzymatic prosthetic ,-roups which reside in the

plastids of leaves and are primarily involved in photo-

synthesis. They do not act in respiratory processes as

do other groups of cytochromes (55, 126). Enzymes having

non-heme iron are succinic dehydrogenase and aconitase

(38, 130).

With ATP, the phosphorylation of amino acids can

then proceed in making the protein portion of chloro-

plasts, enzymes, and other structural proteins (103). In

this way iron is involved in protein synthesis. Pesur

et al. (115) stressed that iron is also essential for

initiating synthesis of chloroplastic protein.

The components of the porphyrin structure, the

skeleton of iron-porphyrin complex, and the Tragnesium-

porphyrin complex, are four pyrrole rings. The carbon

and nitrogen constituents are from glycine and succinate

(38). In the presence of sufficient iron, the copro-

porphyrinogen will be metabolized into protoporphyrinoi-en

which can convert the coproporphyrin to a porphyrin

structure. Carell and Price (36) used. -amino levulinic

acid to substitute for glycine and succinate as raw

material and did synthesize the 6-amino levalinic acid

to porphyrin in the presence of iron. The synthesis

of a porphyrin molecule needs high energy, such as found

in high enerTy phosphate bonds (17, 36, 99).

Iron oxidation states have a -rry significant

influence on some physiological differentiation. Brown

ct al. (26) pointed out that during cell division of the

root tip, iron can either promote or prohibit root

growth depending on the assimilated iron oxidation form

involved. He indicated again that if Fe2' had oxidized

to Fe3*, or simply by removing the less stable Fe2+ by

means of an external chelating agent, the cell division

will be hampered.

The relationship between iron and chlorophyll

synthesis is not fully understood yet (24, 104, 139), but,

is none-the-less a very interesting field. In studying

the green color of plant leaves, it was learned that

chlorophyll pigments occur as lipoprotein complexes with

chloroplast. In fact, 30 to 40 percent of the total nitro-

gen of an oat plant is found in the chloroplasts (155).

Chlorophyl-a is common to all plants and it contains

about 10 percent of the total plant magnesium. The angio-

sperm seedling contains very small amounts of protochloro-

phyll in the darkness. However, when placed under illumi-

nation there is a conversion of chlorophyll-a from proto-

chlorophyll in a few minutes (38, 155). This reaction is

a type of photochemical reaction which can be completed

even under relatively low light intensity. The difference

between protochlorophyll and chlorophyll is that the former

lacks two hydrogen atons in one of its pyrrole rings (14).

The gymnosperm seedling has its protochlorophyll

converted to chlorophyll-a through enzymatic reaction

and therefore this reaction can be completed with no

light (155). Do,.-orr. (14) observed that the conversion

of protochlorophyll to chlorophyll is not a chemical

process either in light or darkness, since his value for

Q10 in excised barley seedlings showed that in the dark
at temperatures of11.00 C. to 23.50 C., Q10 was 1.69; and

above 23.50 C., QI0 was much smaller. In wheat, Q10 was

less than 1.0 when temperature was raising from 25.0

35.00 C. (14). At higher temperatures, chlorophyll produc-
tion usually declined. It was suggested that a higher

temperature resulted in the destruction of the proto-

chlorophyll or converted the protochlorophyll to new

colorless compounds (14, 155).

Some direct correlations between total iron

content and chlorophyll content in the plants have been

found (80). Price and Carell (116) indicated that in

IUlcone the chlorophyll is linearly dependent on the

iron content of the cells. No correlation was reported

between total iron content and that of chlorophyll in

the sunflower plants (80, 81) and others (35, 60, 80,

113, 126). Jacobson (80) reviewed more or less the same
amounts of iron in chlorotic leaves as in ercen leaves.

However, scientists have devisei a workable term, active

iron, which is based on the availability of iron rather

than the total amount of iron in a plant (80, 113).

Active iron is that iron related to the concentration of

chlorophyll (80). Oserkowsky (113) defined active iron

as the iron extracted by 1.0 N Ti103. Active iron is

present in relatively small amounts. For example, 0.3

to 0.5 ag. iron in 1.0 ,im. fresh tissue was enough to

keep pineapple plants ._renish, because the iron was

localized in the chloroplasts (126). The chloroplast

elso contains acid soluble iron, which is not active

iron (127).

The non-chloroplast iron and chloroplast-acid-

soluble iron of the cells are both inactive iron. They

remain approximately constant as long as iron is a

limiting factor. When iron is supplied liberally it

accumulates more rapidly in the non-chloroplast fraction

of the cell than in the chloroplasts (80, 81). Active

iron can be transformed into residual iron, from which

state it can not be utilized for chlorophyll formation

(26). Pesur et al. (115) and others (77, 80) sl,:Zested

that active iron was in organic combinations in the

chloroplasts, and that it did affect the chloroplastic

protein synthesis. Active iron, in the Fe2+ form (26,

140), may be oxidized into Fe3+ and then inactivated in

protein combinations, followed by a disturbance in the

protective protein-chlorophyll combination (140).

Tho failure of the assimilation of iron in plants
load to a number Of disordora, suoh as, inaotivation of
iron porphyrin encymea (36, 154) and iron chlorosio (90,
116,154) on the one handle iron toxicity (70, 07, 119) on
tho other.
Amon the iron porphyrin encyr.os, oytoohro-or.

o, b6, and f are rolatod to the chlorophyll cynthlcis,
that is, oytoohroao o aoto in the electron transport
oyctem of respiratory oyolo which provides cnorey for
the synthesis of protoin-ohlorophyll combination (55,

155); Gytocohrozos b6 and f are vital in the elootron
transport oyatem of photophosphorylation which is also
rolatod to chlorophyll formation as propoood by Evan

(55) HIe discussed oytoohrome b6 and f in using the
follou~in4 photophosphorylation soho.e


2 Cytochromes? 2
H20 t
hloroplast Ascorbate
cm AMP

2 (H)


2 (H)
2 (H)

lie suf:fjested that the ph7otolysis of water

produce bound oxyrenl andl bound hylro rin atonir:. Two

hydro-rn will ro tlro ug the electron transport system,

F.11.N., Vit. K, ascorbate, and. cytochromes to meet the

bound oxygen and form a molecule of water. If a cyto-

chrome, such as cytochrome f, is insufficient, this

process would not be completed and the bound oxygen

atoms would remain with the chloroplast. The chloro-

plasts, and a limited amount of cytochrome f, would be

oxidized and finally destroyed, if there were insuffi-

cient available iron. (v5,n (55) pointed out that it

seems highly probable that cytochrome f is the major

constituent influenced by iron deficiency, because it

has the higheist concentration, 10-5 M, amonnr the

cytochromes groLp in normal plants.

Po,,nnipeuma (119) has reviewed a great many

cases of iron toxicity in plants. Rice in culture

solution with iron concentrations greater than 50 ppm

had the growth and number of tillers reduced. The

Hungary browning. disease of rice is associated with an

excess of reduced iron. The nodal discoloration in

yorng corn plants was due to clogginm of conducting

tissue with ferrous iron. The disease "kalimati" in

sugar cane is believed to be due to ferrous iron

toxicity. These and other physiological diseases

induced by iron toxicity can be cured by an appropriate

addition of potassium fertilizer. They may just as

well be called potassium deficiency diseases.

Factors affecting assimilation of iron in plants,

Potassium occurs mainly in ionic form in the

cell vacuoles and, generally, it is the most abundant

cation in the cell (105). Therefore, numerous pheno-

menon performed in the cell are associated with the

potassium ion through enzymatic reactions (150). Lawton

and Cook (93) pointed out that a number of enzymatic

effects involving the transfer of the phosphate group

of the phosphate pyruvate to the adenylic system in-

volves potassium. This adenylic system involves high

energy phosphate bond formations which act on the

synthesis of proteins and porphyrins. Lawton and Cook

(93) stated that potassium affects photosynthesis and

other physiological processes indirectly through its

influence on chlorophyll components. Often the reduc-

tion of nitrate takes place anywhere iron exists and the

iron will most probably suffer a decrease in solubility

following the reduction of nitrate (119). Potassium

favors nitrate reduction (132). Therefore, a high

concentration of nitrates accompanying a high concentra-

tion of potassium in the plant system means that the

assimilation of iron becomes a problem (132). Bollard

(15) stated that an accumulation of ferric iron would

result from a reduction of nitrates in plants. Lawton

and Cook (93) stated that potassium aided in nitrate

reduction for the ,nt.iihesis of protein particularly in

meristemic tissues. There have been observations that

ammonia-nitrogen resulted in the formation of greater

quantities of chlorophyll than nitrate-nitrogen (124,

126). Jones (86) found traces of chlorosis in potted

gardenia at soil temperatures of 220 to 200 C., distinc-

tive chlorosis at 180 C., and increasingly severe

chlorosis at still lower temperatures. He found no

deficiency in any nutrient elements, and even greater

concentrations of some elements in the chlorotic leaves.

Davidson (45) cured foliar chlorosis of gardenia induced

by low soil temperatures of 150 C. or 200 C., by in-

creasing light intensity, length of day, as well as,

air temperature. During cold nights, nitrate reduction

is at a minimum level of activity, while in the daytime,

conditions will favor highest levels of activity of

the nitrate reductase (109). This may result in the

inactivation of iron assimilation (15).

There seems to be some uncertainty as to whether

there is a greater total organic acid content in chlor-

otic leaves of plants or in non-chlorotic leaves.

Elliott (53) reported greater concentration of aliphatic

acids in non-chlorotic barley shoots than chlorotic

shoots. But Iljin (76) and others (131, 133) found a

large amount of organic acid in chlorotic leaves of

grapes and other plants. A greater concentration of

total organic acids in non-chlorotic leaves than in

chlorotic leaves would indicate both good translocation

and good assimilation of iron, while a greater concen-

tration of organic acids in chlorotic leaves could

indicate the reverse.

Shear et al. (124) found that excess oxalic

acid in the leaves of tung tree influenced iron utiliza-

tion. This oxalic acid production was highly related

to nitrate-nitro-en fertilization (59, 100) and could

be counteracted by the application of calcium (59).

Citric acid is usually higher in concentration in

chlorotic plants than non-chlorotic plants. Iljin

found this true in grape trees (76, 77), Brown et al.

(28) in soybeans, and McGeorge (100) in other plants.

The presence of citric acid affects iron assimilation

in some ways which are not yet known. The research on

soybean and other plants (80, 133, 134) indicated that

chlorotic leaves contained higher amounts of citric

acid than that of the non-chlorotic. The production of

citric acid in the fruit was highly related to potassium

fertilization (39, 82). In the guayule plant, high

citric acid was associated with himh potassium fortili-

zation (39, 40). Malic acid is usually in higher con-

centration in chlorotic plants than in non-chlorotic.

Elliott (53) reported that of the acids found in

chlorotic barley shoots, malic acid was 370 me./,m, of

fresh weight, while citric acid and succinic acids

were 35 ms./gm. and 5 mg./r-1i., respectively.

Burstrom (34) reviewed the function of malic

acid in the metabolism of nations, and reported that it

acts as a malate ion:

malic acid i- ialate- + 211+

If an excess of cations is added to such a

system, the reaction goes to the right, and then an

amount of palate equivalent to the cation excess is

withdrawn from the respiration cycle. Potassium malate

probably is the common potassium organic salt in cell.

Iron malate can also be forced in the cell and the iron

can not be freed from the salt by substitution of zinc

and iia.,=rnese (95). The amount of malic acid increases

with increases in bicarbonate ions and simultaneously

the amount of iron decreases.

Brown (28) found that chlorotic soybean (PI

54619-5-1) was higher in aspartic acid and aspara.-iie

than other varieties. Noggle (110) noticed that chlor-

otic plants were higher in glutamine, lysine, aspartic

acid, and asparagine, but non-chlorotic plants were

higher in alanine, glutamic acid, and glycine. Another

report (28) stated that chlorotic bean plants were high

in aspartic acid and glutamic acid. It is quite certain

that the dicarboxylic amino acids and their derivatives

affect iron assimilation to a noticeable extent.

The concentration of reducing sugar is usually

high in photosynthetic sites of the leaves (28, 30, 40).

The amount of reducing suai.r in leaves was somewhat

proportional to iron assimilation as reported by Brown

(28). He found that the chlorotic soybean contained

slightly less reducing sugar than non-chlorotic plants.

An experiment (127) on grass carried out in culture

solution with high iron content resulted in greater

amount of sugar in plants than did a non-iron culture

solution. Both sug-ested that iron and reducing sugar

were directly related.


In attempts to determine tlhe effects of night

temperature and potassium fertilization on the absorp-

tion, translocation, and assimilation of iron in

centipedejrass, a series of five ,.re.-nhouse-cold

chamber experiments were conducted from 1963 to 196

Descriptions of the experiments and of the laboratory

analyses of soils and plant materials therefrom are

given in the following sections.

Greenhouse-Cold Chamber Experiments

Experiment 1.--Cores of slightly chlorotic

centipedegrass growing on Arredondo loamy fine sand were

transferred from turf plots at the University of Florida

Horticultural Unit to 11 ca. diameter plastic pots in

the greenhouse. After a three-week period of acclima-

tion, the grass was clipped to a uniform height of 1

inch, and the 800 gm. of soil in each pot was brought

to a uniform moisture content of approximately 80

percent of field capacity. Some physical and chemical

properties of the Arredondo soil used in this experiment

are given in Table 1.

The treatments consisted of three rates each of

potassium sulfate and potassium chloride and three

night temperatures. All treatments were replicated

three times. The potassium rates were equivalent to

2, 5, and 8 pounds of potassium per 1,000 square feet.

Other nutrients were uniformly applied in amounts

equivalent to 8 pounds of nitrogen as calcium nitrate,

2 pounds of phosphorus as monocalcium phosphate, and 0.1

pound of iron as monosodium ferric diethylenc-triamine-

pentaacetate (NaFeDTPA) per 1,000 square feet. The

grass was grown in the greenhouse during daylight hours

at daily maximum temperatures ranging from 26.5 to 36.50

C. At night, one-third of the pots was placed in a cold

chamber maintained at 1.60 C., another third was trans-

ferred to a chamber maintained at 7.2 C., and the

re-in~ r. pots were left in the -reenhouse proper, where

the night temperature ran_;:.- from 15.5 to 21.00 C.

Grasses grown at the two low ni-ht temperatures were

placed in chambers at 8:00 P.N. and removed at 7:00 A.I.

each day. In an attempt to maintain uniform humidity

conditions for all treatments, pots were encased in

plastic bags during the night.

Grasses were watered as needed and grown for

eight weeks. At this time, the above-ground portion of

the plant was harvested. The vegetative materials were

dried for 48 hours at 700 C., weighed, and analyzed for

iron, potassium, calcium, magnesiumm, and phosphorus,






O '

0U 0

P 0


1 *





"N N
C) C

T *



cI F
( 9


0 r


usiiLn methods described in I. ",oml-.or:: An.'.Tlyc.'~.

.~epriment 2.--This factorial experiment, con-

sisting of two levels of potanssiui (0 and 2314 ppm) and

two night temperatures (50 and 20-25 C.), with six

replications, was conducted on centipedegrass in acid-

washed sand. Ten plus of grass were planted in 1,000

ml. b c.:ers containing 800 ,ri. of dry sand,after the

soil had been removed by washing. The beakers were

wrapped with aluminum foil, 300 ml. of Hoagland solution

(67) added, and the grass allowed to acclimate in the

greenhouse for 3 weeks. The nutrient solutions, con-

taining the two rates of potassium, were added to the

beakers at 50 mls. per day so as to sustain growth of

grass. After the grass was established, 50 ml. aliquots

of iron solution containing 2.575Ac& of Fe59 in FeC13

were applied to the beakers. .inor elements were added

uniformly to both potassium nutrient solutions, at rates

suggested by Hoagland (67). Iron was added as the che-

late, NaFeDTPA.

The nutrient contents of the two solutions--

with and without potassium--are given in Table 2.

To obtain the night temperature treatments, one-

half of the beakers were transferred to a cold chamber,

maintained at 50 C., at 8:00 P.H. and removed at 7:00

A.M. the next day. The remaining beakers were left in

the greenhouse at night, where the tenopor-iturc varied

froi 20 to 250 C. All pots were kept in the greenhouse

during daylight hours whore daily maximum t.'ipleratures

varied between 35.0 and 42.00 C.

Table 2.--The composition of Toagland nutrient
solutions with and without potassium.

Solution Soluition
Component with Potassium without Potassiur:
ml./1. ml./1.

M i.CS04 2 2

V Ca (I03) 2.4IT20 5 5

0.05 M Ca(H2P04)2II20 -- 10

SKCNO 5 --

M IC2PO4 1 --

The plants were harvested two replicates at

a time on July 6, July 18, and July 30, 1964, after

12, 24, and 36 days of treatment, respectively. At

harvest, the entire plant plus sand was dumped onto a

screen-covered .-r, il and the Fe59-contaminated sand

washed from the roots with a fine stream of distilled


Experiments 3, 4, and 5.--Three uniform

experiments similar to c::piriment 1 were conducted in

the greenhouse and cold chambers; one in the spring

of 1964, one in the suumier of 1964, and the third in

the winter of 1964. The treatments used in each of

the three experiments were the same, except that the

daytime teripcr.tures and the night temperatures in

the greenhouse varied from season to season.

In these experiments, as in Experiment 1,

centipedegrass growing- in Arredondo loamy fine sand

at the Horticultural Unit (Table 1) was transplanted

to 11 cm. plastic pots. Three weeks after trans-

planting, the grass was treated with the equivalent

of 2, 5, and 8 pounds of potassium per 1,000 square

feet, from potassium chloride. At each level of

potassium, two rates of iron equivalent to 0 and 0.1

pound per 1,000 square feet were added as the chelate


The day and nighttime temperatures prevailing

inside the greenhouse during the period of the exper-

iments are given in Table 3.

The temperatures inside the two cold chambers

were maintained at -1.10C. or 7.20C.

After two months of growth, whole plants

were removed from pots, soil washed from the roots

and the plants separated into roots, stems, and

leaves. The plant materials were dried, wei-hed,

and analyzed for inor.-.nic constituents; fresh plant

materials were used for organic constituents, both as

outlined below.

Table 3.
Average Maximum and Minimum greenhouse temperatures

Ave, night temperature Ave. day t-emperature
Season mrax. min. may. ;7in.
oC. oC. C. UC.

Spring, 1964 21.0 18.0 39.7 21.0

Summer, 1964 26.5 22.0 48.0 26.5

Winter, 1964 17.7 16.0 28.6 17.7

,i ., m 1 -A,
-. ,- .. L |

Soil used in experiments 1, 3, 4, and 5 was

Arredondo loamy fine sand, a phospha.bic soil. Some of

the chemical properties of this soil before treatment

were given in Table 1. Soil samples were taken from

individual pots at the termination of the experiments

and used for determination of moisture content and for

chemical analyses. Soil pTf was measured with a glass

electrode-potentiometer at a soil-water ratio of 1:2.

Available nutrients were extracted by shaking 5 gm. of

soil for 30 minutes in 25 ml. of ammonium acetate

solution buffered at pHI 4.8. Calcium and potassium in

the extract were determined by flame at 622 and 670

n/m, respectively, using a Beckman model B flame

spectro-photometer with an oxygen-acetylene burner

assembly. Phosphorus was determined by a modified

ammonium molybdato-stannous chloride procedure (143).

Ex-chnol-rnble f--rror's iron was extracted by a

modification of the procedure described by Jackson (78).

In this modified procr'diir', a 25 -ri. sample of fresh

soil was placed in a 500 ml. flask, shaken for 2 minutes,

with 200 ml. of E ammonium acetate buffered at pTI 6.0,

and filtered into a 400 ml. beaker. A second extrac-

tion was made with 50 ml. of the solution. The filtrates

were combined and evaporated to dryness. An aliquot of

20 ml. of aqua re-ga rwas added and the solution was

again brought to drynrss. The reside pnced in a

muffle furnace and ignited at 5000 C. iui i2 minutes.

After cooling, 3 ml. of concentrated hydrochloric acid

were added, the contents were heated until colorless and

then brought up to 100 ml. with 0.1 11 hydrochloric acid.

A 5 ml. aliquot was employed for the iron determination

by the o-phenanthroline method (85).

The combined exchangeable ferrous and ferric

iron and dilute acid soluble iron in soil were extracted

by N ammonium acetate at pH 3.0 as described by Jackson

(78). Iron was determined by the o-phenanthroline

method (85).

Nitrates were determined by the mitrophenoldi-

sulfonic acid colorimetric method (78) and read on the

Dausch and Lomb S['eetronic 20 colorimeter at 410 mT.


Plant samples analyzed for inorganic constitu-

ents were dried and ground in a Wiley mill to pass a

20-mesh sieve. One ;-rnm of dry plant material was

ashed in a muffle furnace at 5000 C. The ashed material

was di,_ -ted in 20 ml. of 40 percent hydrochloric acid.

After evaporating to dryness on a hot plate, or-onric

matter was removed by heating further with 2 ml. of

concentrated nitric acid. The anh was taken up by 0.1

N hydrochloric acid to 100 ml. Aliquots were used for

determinations of inorganic elements. Calcium was

determined by a turbidimetric method described by Peach

and English (114). i'-gnesium was determined by a color-

imetric method provided by .;iplich (102). Potassium and

phosphorus were determined on the spectrophotometer in

the same manner as used for soil samples. Iron deter-

minations were made by the o-phenanthroline method (85).

Separate samples were used for total nitrogen determi-

nations by the Kjeldahl-Gunning procedure (4).

The determination of Fe59 in the plant was made

by dry-ashing 1 gm. oven-dry plant material. The ashed

material was taken up in 10 ml. of 0.1 N hydrochloric

acid. Duplicated 0.5 ml. aliquots of this solution were

pipetted into aluminum planchets, and dried under an

infrared light, counted on a Geiger-MAller counter and

recorded as counts per minute per gm. of dry material.

Other amino acid and organic acid determinations

were made on fresh plant materials. The fresh tissues

were washed clean with distilled water and excess mois-

ture blotted off. Tissues were separated into leaves,

stolons, and roots and for the extraction of organic acids

10 gm. of leaves, 6 gm. of stolons, and 12 gm. of root

tissue were macerated for 7 minutes in a Waring blender

with 200, 150, and 100 ml., respectively, of boiling 85

percent ethyl alcohol. The material was filtered through

double cheese cloth into a 400 ml. beaker and the residues

remacerated twice with 50 ml. of hot 85 percent ethyl

alcohol and added to the first filtrate. The combined

filtrate was evaporated under the hood to about 25 ml.

and then centrifuged at a speed of 12,000 rpm for 10

minutes. The pellets were centrifuged with 20 ml. of

distilled water. The centrifugate was again reduced

to about 25 ml. The reduced centrifugate was poured

into cation exchange columns, 12 in. long by 0.5 in. in

diameter and containing 5 gm. of Dowex 50-X8 resin with

a small pad of glass wool at the bottom. The column

was washed with 100 ml. of distilled water. The eluate

containing organic acids minus amino acids was collected

and evaporated to about 25 ml. Hereinafter, amino acids

will be reported and discussed separately from other

organic acids. The amino acids which adsorbed on the

cation exchange resin were leached out of the column

with 100 ml. of 2T_ ammonium hydroxide and the eluate

evaporated to dryness. The dried amino acids sample

uas taken up by 1 ml. of 10 percent isopropanol.

The organic acid eluate after being; reduced to

25 ml. volume was poured into an anion exchange column

containing 3 gm. Dowex 1-X8 resin which had been con-

verted to the format form. The column was then washed

with 100 ml. of distilled water. All washing solutions

were discarded. The orr-anic acids absorbed on the anion

exchange resin were leached out with 50 ml. of 50

percent formic acid. The eluate was dried and taken up

with 1 ml. of 10 percent isopropanol.

Amino acids were spotted on Whatman No. 1 filter

paper. The chromatogram was developed according to

Block. et al. (13) and Laurence. et al. (92). The

procedure was slightly modified so that 5, 5, and 10

microliters of leaves, stolons, and roots amino acid

extracts, respectively, were spotted on paper strips.

The strips were run through 75 percent phenol for 15

hours, then dried under a hood for at least 36 hours

before dipping into 0.1 percent ninhydrin isopropanol

solution. The over-spotting technique (13) was employed

to identify individual amino acid. The spots were cut

out and dissolved in 3 ml. of 50 percent ethyl alcohol.

After 30 minutes the color of the solution was measured

with the Spectronic 20 colorimeter at 560 m, A similar-

size area from a region of the paper which has been

dipped in ninhydrin but which had not been traversed by

amino acids was cut out to serve as blank.

Organic acid extracts were chromatographed in

about the same manner as the amino acid. However, there

were differences in sample size for spots and in the

solvent and color developer. The spotting sizes for

leaves, stolons, and roots were 15, 15, and 30 micro-

liters, respectively. The solvent was a mixture of

butanol, formic acid, and water in a ratio of 12:2:15

(13). The color developer was prepared from 1 gn.
xylose, 1 ml. aniline and 3 ml. water diluted to 100

ml. with isopropanol (13). The colored spots were

dissolved with 3 ml. of 50 percent ethyl alcohol and the

color intensity was measured at 395 ma on the Spectronic


Free sugars were crtracted from 1 gm. of dry

and finely ground plant material, according to the

method described by Traub and Slattery (1i:2L The reduc-

ing sugar content of monosaccharides of the extract was

determined by Brown's (30) modification of the Smogyi's

semi-micro copper method (30). The determination of

cold water soluble carbohydrates was also made using

the hydrolyzate from the previous extraction and using

the same procedure as that used for reducing sugars.

The ferric cyanide reduction method described

by Brown et al. (28)was used to determine the reductive

capacity of centipedegrass roots. In this procedure,

75 ml. of aerated 10-4 G IKFe(CN)6 and 5 ml. of 10-6

M FeC13 were placed in a 125 ml. flask. Ten pieces of

grass roots were inserted in the solution. The degree

of reduction of the mixtures was determined on the

colorimeter at 400 mUevery 12 hours. Data were re-

corded as optical density change per 12 hours per gm.

of dry material.

Root cation exchange capacity was determined

by the method described by Drake. et al. (50) in which

fresh grass roots were dialyzed for 72 hours. They

were thoroughly rinsed with distilled water and then

centrifuged at 2,000 rpm for 5 minutes to provide the

roots with approximately equrl moisture content. A 3 gm.

sample of the centrifuged roots was mixed with 150 ml.

of KC1 in a beaker for 30 minutes. The roots-KC1 system

was titrated with 0.05 L IKOH to pH 7.0, as measured by

a glass electrode. The weights of roots were determined

after drying for 48 hours at 900 C. in the oven.


Experiment 1

Neither sources nor rates of potassium fertili-

zer had significant effect on the growth of centipede-

grasses, as reflected by yields shown in Table 23. The

yield of grass grown at the prevailing night temperatures

in the greenhouse (15.5 21.00 C.) averaged from 25 to

40 percent greater than grass kept in the cold chamber

at night at the two lower temperatures. However, there

was no significant difference between yield of grass

maintained at 1.60 C. and that of grass maintained at

7.20 C. during night hours. It should be pointed out

that no chlorosis was observed regardless of treatment

probably because iron chelate was added uniformly to

all pots. However, leaves of grass grown at the low

night temperatures were short along the mid-rib and

exhibited a purpling of the margins.

The concentration of iron (Table 21) in grass

grown at two low night temperatures (1.60 C. rind 7.20

C.) was greater than in grass kept in the greenhouse

continuously, as shown in Figure 1. Increasing rates

of potassium sulfate did not affect iron absorption,

except at the lowest night temperature, 1.60 C., but

Fe, ppm

-1 -4
0 :r



- -h
4 Z

C -D




r* 0

0 *V





_I- %v v0 0
0 V ) 0 VI 0

K, mgm

o V o 0 0

K, percent

Fe, mgm


I0 I 0

I/ I

/ I \n -

I co

/ 0
S. S
v 2 -----a s -- -

- k

increasing rates of potassium chloride generally

reduced iron absorption at all three night temperatures

(Table 21). It therefore appears that the anion compo-

nents of the potassium salts played a more important

role in iron absorption than the potassium itself, and

that the chloride ion influenced iron uptake more than

did the sulfate ion, at the three levels of potassium

used (Figure 2).

Total amount of iron absorbed by the gracs was

not affected by the three night temperatures (Figure 1)

as much as the concentration of iron in the plant.

However, total iron content had a tendency to decrease

with increases in potassium levels (Figure 2). There

was a significantly -rroater uptake of iron where the

chloride was used than sulfate (Figure 2).

Percentage potassium in the grass was increased

with increase in the rate of potassium fertilizer, as

shown in Figure 2. The response to potassium sulfate

appearedto be better than that to potassium chloride, at

all three levels. Nevertheless, increases in night

temperature (Figure 1) increased the concentration of

potassium in the plant, regardless of source. The

potassium chloride source resulted in an almost linear

increase, while the potassium sulfate source resulted

in a decrease at the intermediate night temperature and

Fe, ppm

vK o vi o vi
K, percent

Fe, mgm

* *0
vi o

K, mgm

then an increase at the highest temperature (15.5 -

21.00 C.).

The total potassium upt..k-. by the plant

generally increased with added potassium, but the

effect is greater with potassium chloride than

where potassium sulfate was used (Figure 2). Al-

though potassium chloride was taken up fairly well in

the entire temperature range from 1.60 C. to 15.5 -

21.00 C., potassium sulfate absorption was decreased

between 1.60 C. and 7.20 C., but then absorption in-

creased rapidly with increases in temperatures from

7.20 C. to 15.5 21.00 C.

An inverse relationship was observed between

the absorption of potassium and the absorption of

iron. Particularly noteworthy was the effect of

potassium on iron absorption when applied as potas-

sium chloride. This doubtlessly resulted from the

fact that potassium chloride was absorbed more read-

ily by centipedegrass than potassium sulfate, when

these two potassium sources were compared at the

higher rates of application.

Experiment 2

In this sand culture experiment using Fe59,

the yields of centipedegrass groim at the high night

temperature (15.5 22.50 C.) were significantly

Greater than yields at a night temperature of 4.50 C.

(Table 23). This was particularly true of the yield

of above- ronid portions, or tops, as shown in Fiyire

3. The potassium-containing nutrient solution pro-

duced craiter growth of both roots and tops than the

solution without potassium. The -rratest yield of

tops from this nutrient was obtained at the higher

night temperature (Figure 3). The general appear-

ance, or color, of the grass changed from a slight

yellow-green at the beginning of the experiment, to

a very slight yellow-green at the first and second

harvests, to a full green color at the end of 36 days.

The concentration of iron, as expressed by

Fe59 in counts per minute per gm. of oven dry materi-

al, is shown in Table 24. The statistical analysis

showed that there were highly significant differences

in the concentrations of iron between that in the

roots and that in the tops of plants, and that dif-

ferences in iron concentrations were related to rates

of potassium (Table 26). That is, the potassium in

the nutrient solution appeared to decrease the per-

cent of iron in the plant. The magnitude of the de-

crease is shown in Figure 4.

The concentration of iron in the roots,

which contained three to four times more Fe59 than


Yields, gm. of dry material















I K -i

1 1 10
I \I

Ir VI 0
00 0
In 0

Q1 0



- F.I

Yields, gm. of dry material

M O O Co
o o O O

0 0

I U3
I N)


( t



, *



n i31

the tops, was greatly affected by the use of potassium

in the nutrient solution. The concentration of iron

in the grass was generally less at the higher night

temperatures, and the effect of potassium on Iron

content was greater at these temperatures than at the

lower temperature. On the other hand, there was little

difference in iron content of tops of plants Crown at

the two night temperatures. The potassium addition had

no effect on the content of iron at the 15.5 22.50 C.

night temperature, and only slightly reduced the iron

content at the low night temperature. It seemed there-

fore, that potassium decreased the iron uptake in the

roots through some mechanisms of competition for absorb-

ing sites of the roots. Once the iron, or iron chelate

molecule, entered the root it was apparently no longer

affected by the presence of potassium at the higher

night temperatures, and it was only slightly affected

at the low night temperature (4.50 C.).

Total iron content, a product of concentration

and yield, in the tops of the plants was decreased with

the application of potassium at 4.5 C., but increased

at high night temperatures (15.5 22.50 C.). However,

the reverse was true for the roots ( 4). This

suggests that at the 4.50 C. the potassium application

slightly increased the growth of roots (Figure 3) and

o 0 0 0

EOl X I 'lepjajew A/p w6/u!w/ (6,.A) sjuno3


I *
SjLA 0.

I w



I/ / II

I/ / I
/ I

W % *
SX ( ) sun o

EOt X I *Ie!jaem Ajp uwi/u!w/ ( s5a) slunoQ









- 0.
( 3Q






4- 0



4- C


4- 0
0 w



increased the total uptake of iron by the roots; but

this iron was not readily translocated to the top of

the plant. At high night temperatures roots continu-

ously took up iron, due to increased root activity, and

the iron was rapidly translocated to the tops, as a

result by the greater growth of that portion of plant.

Furthermore, as indicated by the three consecutive

harvests, the total iron content of tops of the plants

progressively increased at both temperatures, with or

without potassium (Figure 5). This increase in iron

may be at the expense of the iron content of the roots,

as indicated in Figure 5.

The percentage of potassium in the grass was

highly significantly influenced by the application of

potassium to the solution. Moreover, the concentration

of potassium in the tops was greater than that in the

roots (Table 25). Total potassium uptake in the tops

rapidly increased during the three consecutive growth

periods, just as total iron content increased in that

portion of the plant.

The following facts may be gathered from the

results of this experiment. (a) High night temperatures

(15.5 22.50 C.), or the application of potassium,

increased the yield of tops and roots of centipedegrass,

but affected the tops of the plants more than the roots.











12 24 36

Growth period in days

Figure 5.

Total Iron (Fe59) and Potassium
Contained in Tops and Roots of
Centipedegrass at Three Growth








*"W..t Root

%.a.. -0-00

(b) The potassium application decreased the concentra-

tion of iron in the roots, particularly at high night

te;pnratures (15.5 22.50 C.). (c) The potassium

application decrcrqs- the total iron content of the

tops of the plants at low night temperature (4.50 C.)

but increased at higher night temperature. The total

iron content in the roots was decreased at the higher

night temperatures and increased at low night tempera-

ture. (d) Total iron content and total potassium

content in the tops of the plants increased as a grass

matured, while the total iron and total potassium of

the roots decreased with the progressive growths.

Experiments 3. 4, and 5

Experiments 3, 4, and 5 were similar in all

respects, except that they were conducted in three

different seasons, and for this reason their results

are presented and discussed together. The temperatures

for the three seasons, expressed as the averaged

maximum temperature for daylight hours, are shown in

Table 3. While the night temperature in the greenhouse

varied with seasons, the two cold-chamber night temper-

atures were maintained at -1.10 C. and 7.20 C. for all

three seasons.

Plant Growth

Plant appearances developed during the progress

of these experiments were significantly related to

treatments. In general, plants that received iron

chelate, NaFeDTPA, varied from very slightly yellowish-

green at night temperature of -1.10 C. to dark green

for those at 7.20 C. and 18.0 22.50 C., as shown in

Figure 6. Figure 7 shows representative pots of the

series of treatments in which no iron chelate was

applied to the soils. The grass appeared green in the

high temperatures, but the three potassium treatments

which were kept at -1.10 C. during the night had a

definite yellowish-green appearance. The application


Fig. 6.--Effects of Night Temperatures and
Rates of Potassium in the presence of Added Iron on
the Appearance of Centipedegrass,

Notes Jisht temperatures TI = -1.10 C., T2 = 7.20 C.,
T3 = 18.0 25.0 C.
Potassium rates: Ki = 2 lbs., K2 = 5 lbs.,
K3 = 8 Ibs., per 1000 sq. ft.
Iron rates: Fe1 = 0.1 lb. of iron, as a
chelate, per 1000 sq. ft.

A1. 7.--Effects of ':liht temperatures and
Rates of Fotassium in the absence of Added Iron on
the Appearance of Centipedegrass.

,;otes ?or lese nd see Fi3. 6.

of potassium fertilizer slightly intensified the devel-

opment of the yellow color.

The leaves of centipedegrass which received

the different treatments varied in size, as shown in

Figure 8. Leaves in this photograph were taken from

the third leaf position back from the apex of a random

sample from each treatment. At a night temperature of

-1.1o C. the leaves were all smaller than those at the

higher night temperatures. Leaves that received an

application of iron (Fel) were generally larger than

leaves without additional iron (Fe0).

An examination into the morphology of the roots

reveals some differences due to treatments. That is,

roots grown at low temperatures were generally white

and soft, while roots grown at higher temperatures were

darker in color, dense and very profused, as shown in

Figure 9. This picture further illustrates that when

comparing each pair in each row, the left one which

received no additional iron (Fe0), grew larger and more

twisted than the mate that received the iron treatment

(Fel). On the other hand, potassium applications did

not appear to affect the morphology of the roots.

Plant yield data in the three experiments are

shown in Table 27, for the leaves, stolons, roots, and

entire plant, respectively. All yields were highly

'I 8,--Sffects of Ni-ht Temperatures,
Rates of Potassium and Iron on leaves of Centi-

;ot o: -or leend see 1, 6.


MSi. 9,--Effects of dIlght Temperaturos.
j atcs 01 0o!.assui arid :ron on :-oots of Centipede-

::oct .'or le: 7end see 71F. '.0

significantly influenced by temperatures, except for

the leaves which were significantly affected (Table 4).

The effect of night temperatures on yields are graphic-

ally presented in Figure 10. Total yields of the plant

increased almost linearly as night temperatures

increased. When the grasses were divided into component

parts, the roots and stolons were found to exhibit

trends in response to night temperature similar to that

of the entire plant. However, leaf growth did not

increase at temperatures above 7.20 C. One might specu-

late, therefore, that plant growth in response to a

warm spell, when night temperatures are between 7.20 C.

to 18.0-25.0o C., is composed of two responses, that of

the stolons and the roots, while from -1.1o C. to 7.20

C., plant growth is a combination of responses of leaves,

stolons, and roots. These findings are somewhat

different from the findings in the sand culture experi-

ment in which leaf growth responded to warm night

temperatures more than the roots. The yields of stolons

as well as the yields of the entire plant were signifi-

cantly different among the seasons as shown graphically

in Figure 10. In general, the yields associated with

the summer, or highest average daylight temperatures,

and those associated with the winter, or the lowest

temperatures, were about 20 to 30 percent less than







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yields produced at the intermediate daylight tempera-

tures prevalent during the spring period.

A highly significant interaction was observed

between temperatures and applied iron on the growth of

roots (Figure 11). At both the high night temperatures

(18.0 25.00 C.) and the low night temperatures (-1.10

C.) root growth was less for grass that received an

iron application as compared to grass that received no

iron treatment.

Potassium had a tendency to increase plant

growth, as shown in Figure 12. However, this increased

growth was mostly a result of root growth, since the

root was the only component which increased in growth

with increases in potassium.

Plant Inorganic Constituents

Iron contents of grass in the three experiments

are tabulated in Table 28. The analyses of variance

(Table 4) showed that night temperatures significantly

affected the iron concentrations in all parts of the

grass. The iron concentration in plant parts was also

markedly affected by night temperatures, seasons, rates

of potassium, and rates of iron, as shown in Table 5.

There was a definite tendency for the iron to decrease

with increases in night temperatures. However, total

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iron in the entire plant (Table 5) increased with

advanced night temperatures. The distribution of iron

within the three major parts of the grass was employed

as an indication of iron translocation. An examination

of the data shows that there was no change in distribu-

tion under the three different night temperature regimes.

Therefore, translocation seems to have operated inde-

pendently of night temperatures. The averaged distri-

bution of plant total iron among leaves, stolons, and

roots for centipedegrass was 26.6, 22.5, and 50.9

percent. This indicates that one-half of the absorbed

iron was stored in the roots and only one-quarter was

transferred to leaves.

Iron absorption and distribution were affected

tremendously in all three parts of the plant by season

in which the experiment was conducted. In the summer

of 1964, when the average daily maximum temperature

was 48.00 C., the iron concentration was 145, 115, and

287 ppm for leaves, stolons, and roots, respectively.

However, in the winter, with an average daily maximum

temperature of 28.60 C. the iron contents were much

higher; 212, 188, and 394 ppm, for the respective parts.

Considering the entire plant (Table 5), the concentra-

tion of iron was 182 ppm for plantsgrown in the summer,

while it was 263 ppm for plants grown in the winter.









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Total iron absorption by plants grown at the higher

temperature (48.00 C.) was also less than by plants

grown during the winter (28.60 C.). There was no

change in distribution percentages of the iron due to

changes in seasonal temperatures. These data indicate

that neither night temperatures nor seasons affected

iron translocation, but both affected iron absorption.

The rate of potassium application had a signi-

ficant effect on iron concentration in the whole plant

(Table 4). Plants that received the equivalent of 2

lb. of potassium per 1,000 square feet contained 238

ppm of iron, but grass that received 5 and 8 lbs. of

potassium per 1,000 square feet contained only 217 and

215 ppm of iron, respectively (Table 5). However,

total iron uptake was not affected by the rates of


Pots that received the iron chelate treatments

exhibit an increase in the iron concentrations of the

leaves, roots, and entire plants, as compared to pots

to which no iron chelate was applied (Table 5). Calcu-

lations of distribution percentages of the iron from

the chelate show that a considerable portion of added

iron may have been retained in the roots rather than

being translocated to tops of the grass. Nevertheless,

the absolute amount of iron in the tops of the grass to

which iron was supplied was still significantly higher

than in plant tops to which no iron was applied, as

shown in Table 5. Several significant interactions of

applied iron and night temperatures on the iron concen-

trations of centipedegrass are shown in Figure 13.

For example, chelated iron was more effective at the

lowest night temperature than at the higher temperatures,

especially for the roots of centipedegrass.

Potassium contents in the tissue of centipede-

grass are shown in Table 29 and the analyses of variance

are listed in Table 4.

Highly significant differences were found

among night temperatures (Table 4) and their effects

on percent potassium of roots and leaves, and for the

whole plants. The percent potassium in leaves, roots,

and the entire plant grown at the medium night tempera-

ture (7.20 C.) was usually higher than when grown at

the highest night temperatures (18.0 25.00 C.), or

the lowest night temperature (-1.10 C.). However, total

potassium content of grass grown in the greenhouse at

night temperatures of 18.0 25.00 C. (Table 6) was

greater than in grass grown at -1.10 C. or 7.20 C.

The percentage distribution of potassium in the various

parts of the grass may be an indication of the potassium

translocation in that plant, This percentage distribu-



Night temperature in C

Figure 13.

Effects of Night Temperatures and
Rates of Iron on the Iron Content of
Leaves, Roots, and Entire Plants of

tion in the grass roots and stolons was changed with

changes in night temperatures. Relatively speaking, at

night temperature of -1.1 C., the translocation of

potassium from roots to stolons was much faster than at

warmer night temperatures.

The relatively mild winter season with an

average daily maximum temperature of 28.60 C. resulted

in higher concentrations and greater total potassium

absorption than did the hot summer season (48.00 C.),

except for stolons, as indicated by the analysis of

variance in Table 4. Translocation of potassium was

also influenced by the season in which the experiment

was conducted. A larger percentage of potassium was

deposited in the stolons in the summer (30.3 percent)

than in the winter (22.7 percent), as shown in Table 6.

Furthermore, there was a higher percentage potassium

in the leaves during the winter than during the summer.

Increases in amount of applied potassium highly

significantly increased the amounts of absorbed potas-

sium in grass, leaves, and roots. The increases in

potassium rates increased the percent potassium content

of the leaves of the grass grown at -1.1o C. much more

than plants grown at warm night temperatures (Figure 14).
An application of iron decreased plant total

potassium uptake; this decrease was mainly exhibited in


4 -4 mV w02 Nf^P nn nC lvC -t cC-
0 0 ** *
Cd C C Pz rc.C^ a- C r nj- o T-4 0-
04 Csc \0\- cO 0\0 0H0
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Note: Kl= 2 Ibs., K2= 5 lbs., K 8 lbs. of
potassium per 1,000 sq. ft.


= No K2
/ ^~",

^ -^,^_-^.- -

Night temperature in C


Figure 14.

Effect of Rates of Potassium and Night
Temperatures on the Percent Potassium
in Leaves of Centipedegrass.