Increased availability of nutrients is an increasing threat to biodiversity, especially within nutrient limited environments. In temperate grasslands, increases in nitrogen and phosphorus decrease abundance of C4 photosynthetic grasses and increase C3 species. In coastal systems, nutrient studies are limited and do not include functional compositional changes. Barrier islands present a unique opportunity to study the effects of community and functional composition changes due to nutrient enrichment as sandy soils are low in nutrients and have high leaching potential. Further, expansion of a nitrogen-fixing woody species has increased N input into these systems at a rate of ~16 g m-2 yr-1. Our objective was to determine species and functional response of a coastal grassland within the Virginia Coast Reserve, LTER to increased N and P enrichment. We hypothesized that nutrient enrichment would lower species diversity and alter functional composition through increased abundance in C3 species and community weighted specific leaf area. Following a modified experimental design from the Nutrient Network, four treatments were randomly assigned (control, N, P, NP, n = 5), with nutrients added at a rate of 10 g m-2 yr-1. Annual net primary productivity (ANPP), species composition, and functional traits were measured for two years.
Results/Conclusions
Contrary to our hypothesis, nutrient enrichment did not alter species diversity or richness. Over all variable measured, there was no effect of phosphorus or year. ANPP was higher in nitrogen enriched plots only (852 ± 101 g m-2), with increased production in both grasses and forbs. In general, ANPP was higher than expected in a low nutrient system and comparable to other temperate grasslands (control plots, 432 ± 43 g m-2). Percent cover of both C3 and C4 species increased with nitrogen additions, with no dominance of one type occurring. Community weighted specific leaf area (CWSLA) was lower than reported in most grasslands (92 ± 10 cm2 g-1) and only significantly higher in NP plots (181 ± 30 cm2 g-1). CWSLA in NP plots were higher than values found in any barrier island habitat. Although N has a significant impact on cover and ANPP, our results indicate that after two years N and P alone do not alter species or functional composition of coastal grasslands. However, synergistic NP effects alter community level resource allocation and leaf construction, novel functional strategies for adapting to nutrient enrichment. These results can inform community assembly processes in stressful environments.