Phosphorus Enrichment Affects Litter Decomposition, Immobilization, and Soil Microbial Phosphorus in Wetland Mesocosms

Like many wetland ecosystems, areas of the northern Everglades of Florida, USA, have been influenced by P eutrophication. Our objective was to determine if P enrichment of water influences the litter decomposition rate and nutrient immobilization by litter and, further, to determine the quantitative relationship of these responses across a range of P concentrations in surface water. In addition, we determined whether P additions rapidly elevated microbial biomass P in the soil. In order to isolate the effects of P enrichment, we placed bags containing cattail (Typha domengensis Crantz) and sawgrass (Cladium jamaicense Pers.) litter into two sets of experimental channels into which controlled inputs of five different phosphate concentrations were added continuously. After 1 yr of incubation, litter was analyzed for C, P, N, Cu, Ca, and K content. Loss of C at the end of 1 yr increased linearly with increasing average PO4 content in the channels with a similar slope for both species of litter. Immobilization caused an absolute increase in P content of the litter up to approximately ninefold across the range of water P concentrations, while immobilization of N, Ca, and K did not vary with water P concentrations. During decomposition, litter exhibited a net uptake of Cu (a nutrient potentially limiting plant growth on peat soils). The microbial biomass P was up to nine times higher in the surface soil of the most enriched channel compared with the control, but this elevation in concentration was restricted to the upper 12 cm of soil.