SWS-01-2

(s4 Soil and Water Science

Research Brief

PHOSPHORUS LOADING EFFECTS ON EXTRACELLULAR
ENZYME ACTIVITY IN EVERGLADES WETLAND SOILS

A. L. Wright and K. R. Reddy

Wetland soils support a large diversity of
microbial communities that play important
roles in the decomposition of organic matter,
nutrient cycling, and abating the toxic levels
of contaminants. A majority of organic
matter in wetlands is composed of high
molecular weight, polymeric compounds, of
which only a small portion is readily
available to microbial communities.
Complex structural compounds must be first
hydrolyzed through the activity of
extracellular enzymes into low molecular
weight compounds. These low molecular
weight compounds can be directly
transferred to cells, oxidized, and used as an
energy source.

Microbiological properties, including
enzyme activities, can be potentially useful
as indicators of soil and water quality.
Many of these enzymes are affected by
nutrient loading, as bioavailable nutrients
can potentially decrease their activity. Thus,
measurement of extracellular enzyme
activities may be useful for predicting the
impacts of P loading since they are
important to organic matter degradation,

nutrient regeneration, and various elemental
cycles.
The objectives of the study were to
determine; (1) the influence ofP loading to a
wetland on activities of various extracellular
enzymes in detritus and soil, (2) the
relationship between extracellular enzyme
activities and selected microbial and soil
physico-chemical parameters; and (3) to
determine if these enzyme activities are
useful as sensitive indicators of P impacts.
We measured the activity of various
extracellular enzymes in detritus and soil
samples collected along a soil phosphorus
(P) enrichment gradient located in Water
Conservation Area 2A (WCA-2A) of the
Florida Everglades. The extracellular
enzymes assayed were alkaline phosphatase
(APA) (phosphorus cycle) arylsulfatase
(sulfur cycle), (3-d-glucosidase, and phenol
oxidase (carbon cycle), and protease
(nitrogen cycle).
The study site is
WCA-2A of the
Florida
Everglades. This
447 km2
impounded
wetland has
received nutrient-
laden drainage
waters for the past
several decades
from the adjacent
Everglades
Agricultural Area
(EAA). Inflow of these waters has been

implicated in contributing to increased P
concentrations in the soil and water column.
Historically, this system was P limited and
contained a mixture of sawgrass (Cladium
sp.) and slough communities. The addition
of P laden waters and altered hydrology
have been implicated as key factors in a
vegetation shift from the indigenous
sawgrass/slough communities to cattail
(Typha sp.) dominated areas, resulting in
increased peat accumulation and additional
soil and water alterations Soils near the
inflow have the highest P concentrations,
and P concentrations decrease with
increasing distance from the inflow.
Corresponding to changes in soil P
concentrations, a gradient in vegetative type
exists as well. Cattail is the dominant
vegetative type in areas impacted by P,
while sawgrass is prominent in unimpacted
areas.
Alkaline phosphatase activity (APA) was
the only enzyme affected by P loading and

concentrations. The APA appeared to be
regulated by specific soil and microbial P
parameters in detritus and the upper soil
depths. However, relationships between
soil and microbial physico-chemical
properties and other measured extracellular
enzyme activities seldom produced
significant relationships. Alkaline
phosphatase activity appears to be suitable
for use as an indicator of wetland
eutrophication.

Full text of this paper can be found at:
A. L. Wright and K.R. Reddy. 2001.
Influence of phosphorus loading on
extracellular enzyme activity in Everglades
wetland soils. Soil Science Society of
America Journal (in press).

Alkaline Phosphatase Activity
[Water Conservation Area-2A]

oo

o EL

25
20 Impacted Unimpacted
Detritus.*
15, ."

S.0-10 cm
0 ''0-0 c c
0 3 4 7 10 11
0 1 2 3 4 5 6 7 8 9 10 11

Distance from inflow (km)

was negatively related to soil P
concentrations and microbial biomass C and
P. Arylsulfatase, J-d-glucosidase, protease,
and phenol oxidase were not affected by P
loading and were not related to measured
soil C, N, S, and P physical and chemical
parameters. All enzyme activities were
highest in the surface detritus layer and
decreased with soil depth.
Phosphorus loading to an oligotrophic, P
limited wetland had a significant influence
on APA in detritus and soil but not on other
measured extracellular enzyme activities.
Extracellular enzyme activity markedly
decreased with depth in the soil profile, and
detritus was most responsive to changes in P

AUTHORS

A. L. Wright
Soil and Water Science Dept.,
P. O. Box 110510, University of Florida,
Gainesville, FL 32611
Alwr@gnv.ifas.ufl.edu

K.R. Reddy,
Soil and Water Science Dept.,
P. O. Box 110510, University of Florida
Gainesville, FL 32611 krri@ufl.edu

This research was supported by the Florida
Agricultural Experiment Station and a grant
from the South Florida Water Management
District and approved for publication as
Journal Series No. R-07810.

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