| Abstract |
Wetlands constitute a transitional zone between terrestrial and aquatic ecosystems and have unique characteristics such as
frequent inundation, inflow of nutrients from terrestrial ecosystems, presence of plants adapted to grow in water, and soil that is
occasionally oxygen deficient due to saturation. These characteristics and the presence of vegetation determine physical and chemical
properties that affect decomposition rates of organic matter (OM). Decomposition of OM is associated with activities of various
extracellular enzymes (EE) produced by bacteria and fungi. Extracellular enzymes convert macromolecules to simple compounds such
as labile organic carbon (C), nitrogen (N), phosphorus (P), and sulfur (S) that can be easily taken up by microbes and plants. Therefore,
the enzymatic approach is helpful to understand the decomposition rates of OM and nutrient cycling in wetland soils. This paper reviews
the physical and biogeochemical factors that regulate extracellular enzyme activities (EEa) in wetland soils, including those of β-
glucosidase, β-N-acetylglucosaminidase, phosphatase, arylsulfatase, and phenol oxidase that decompose organic matter and release C,
N, P, and S nutrients for microbial and plant growths. Effects of pH, water table, and particle size of OM on EEa were not significantly
different among sites, whereas the influence of temperature on EEa varied depending on microbial acclimation to extreme
temperatures. Addition of C, N, or P affected EEa differently depending on the nutrient state, C:N ratio, limiting factors, and types of
enzymes of wetland soils. Substrate quality influenced EEa more significantly than did other factors. Also, drainage of wetland and
increased temperature due to global climate change can stimulate phenol oxidase activity, and anthropogenic N deposition can enhance
the hydrolytic EEa; these effects increase OM decomposition rates and emissions of CO2 and CH4 from wetland systems. The researches
on the relationship between microbial structures and EE functions, and environmental factors controlling EEa can be helpful to
manipulate wetland ecosystems for treating pollutants and to monitor wetland ecosystem services. |
