Effects of 4 years of nitrogen and phosphorus additions on Everglades plant communities

Nitrogen (5.6 and 22.4 g m(-2) per year) and phosphorus (0.6, 1.2, and 4.8 g m-2 per year) were applied to Everglades plant communities (sawgrass, mixed sawgrass-cattail, slough) to evaluate the effects of nutrient additions on biomass production, photosynthesis, N and P uptake, and species composition. After 2 years, additions of P alone and N+P at a rate of 4.8 g P m(-2) per year resulted in a two- to three-fold increase in biomass at the sawgrass and mixed sawgrass-cattail communities. Additions of P and N+P also increased sawgrass and cattail leaf area index (LAI) two to nine times, resulting in an increase in biomass and ground area photosynthesis. In the slough community, additions of P at the highest rate (4.8 g m(-2) per year) resulted in a 90% loss of the Utricularia-periphyton complex after 1 year, with a concurrent increase of the macroalgae, Chara. After 4 years of P addition at the highest rate, we observed an enrichment of soil easily exchangeable inorganic P and organic P in the sawgrass and slough sites, Fe- and Al-bound inorganic P (sawgrass only), and Ca-bound inorganic P (slough only). There appeared to be cumulative P loading at 10 g m(-2), above which there was no additional increase in biomass production or tissue P uptake by emergent vegetation. However, cumulative P loading of only 5 g m(-2) resulted in near elimination of the Utricularia-periphyton complex. Our results suggest that P loadings alter the Everglades plant communities through increased plant productivity, tissue P storage, soil P enrichment, and shifts in plant species composition (e.g. replacement of the Utricularia-periphyton complex by Chara). Management policies for protecting the Everglades must consider cumulative effects of nutrient loadings, especially P, on changes in native plant communities and enrichment of the soil. (C) 2000 Elsevier Science B.V. All rights reserved.