Ratios of stable N isotopes (δ¹⁵N) have been shown to vary according to P impact δ¹⁵N in plants and soils in an area of the Florida Everglades known as Water Conservation Area 2A (WCA-2A). In this region, impacted plants and soils display isotopic enrichments of up to 6 and 4 ‰, respectively. These δ¹⁵N shifts indicate changes in N cycling as a result of anthropogenic P eutrophication, rather the presence of N pollution described in other isotopic studies. Hypotheses to explain the N isotopic enrichment of WCA-2A plants and soils primarily consist of P effects on plant N uptake or on N mineralization and loss processes in the soil. This work sought to test the mechanisms related to P enhancement of N mineralization and subsequent loss of isotopically light soil N. Bottle incubations of P-amended WCA-2A soils demonstrated significant enhancement of N mineralization through increased ammonium and organic N, but no conclusive ability of loss of these compounds to significantly alter soil δ¹⁵N. This prediction was further tested by isotopic analysis of samples from an in situ 5-year P dosing experiment. Based on these results, WCA-2A isotopic patterns seem better explained by plant processes such as altered nutrient uptake and litter production than those of microbial or geochemical origin. We believed these findings illustrate the isotopic sensitivity of wetland vegetation to shifts between N and P limitation and the dominant role of plants in regulating ecosystem δ¹⁵N patterns through production of detrital matter.