Influence of Phosphorus On Soil Organic Nitrogen Pools in Subtropical Wetlands.

Soil organic nitrogen (SON) is a major source of bioavailable nitrogen (N) to biological communities, and therefore, is an important component of soil organic matter (SOM). In wetland systems, approximately 95% of total soil N is in the form of organic N. Although the importance of SON is recognized, SON is not well characterized. This study compares SON pools along an existing phosphorus (P) gradient, from enriched to unenriched P, in the Water Conservation Area 2A (WCA-2A), Florida Everglades. The WCA-2A has been impacted by anthropogenic drainage, channelization, and nutrient loading that have resulted in a vegetation community shift, as well as long term changes in soil nutrient concentrations. Therefore, we hypothesize that N/P ratios will decrease with increasing P enrichment; however, the proportions of labile and nonlabile pools of SON will not be affected. To test this hypothesis, soil cores were obtained from enriched, intermediate, and unenriched P sites. Soil cores were separated into floc (unconsolidated detrital material), 0-10, 10-20, and 20-30 cm sections. Physico-chemical characteristics of each sample were analyzed for percent moisture, bulk density, loss on ignition, total carbon (C), N, and P, extractable NH₄⁺, potentially mineralizable N (PMN), microbial biomass C and N, and leucine aminopeptidase and β,4-N acetylglucosaminidase hydrolytic N enzymes. Soil organic N pools were determined by the diffusion method, with modification, to separate N pools into total hydrolyzable N, NH₄-N, amino sugar N, amino acid N, and acid insoluble N. In conjunction with gross organic N pools, the use of mass spectrometry resulted in the qualitative identification of specific organic N compounds. Results suggest P enrichment has led to increased PMN rates and in increase in acid hydrolyzable (labile) N. This may affect the overall SON pool and source of N to biological communities, resulting in shifts in ecosystem structure and function.