Nutrient deposition is a global phenomenon that is increasing with persistence of climate change, with increased nitrogen deposition along coastlines. Coastal ecosystems are characterized by low nutrient soils, a predominant driver in plant community structure. On barrier island systems, a change in community structure could alter dominant species, leading to cascading effects such as altered biotic interactions and subsequent response to disturbance events. A knowledge gap remains in understanding how nutrient deposition affects coastal plant communities across temporal scales. Our objective was to investigate effects of nutrient deposition on community level productivity and species dominance. Following a modified Nutrient Network protocol, we established nitrogen (N), phosphorus (P), and reference (R) plots in a full factorial design, producing 4 groups (N, P, R, and NP). Plots were fertilized twice annually, while annual net primary production (ANPP) and species composition were quantified once per year. We hypothesize that ANPP will vary between nutrient treatments, maximized in NP plots, but will remain constant between years. We also hypothesize that increased nutrient additions will cause alter species dominance of each community, increasing the occurrence of C3 species, especially forbs, as nutrients become less limited.
Results/Conclusions
Our data show that ANPP did not vary between years, supporting our hypothesis of interannual consistency, but did vary by reason of altered nutrient addition. ANPP was higher, across all years, in N (864.2 ± 47.9 g m-2 yr-1) and NP (930.2 ± 112.1 g m-2 yr-1) plots compared to P and R plots (383.7 ± 40.5g m-2 yr-1 and 296.53 ± 30.6 g m-2 yr-1, respectively). Our data shows that biomass varied based on growth form, specifically, cover of C3 species was higher in N and NP plots (47.2% and 46.8%, respectively) than in P and R plots (25.9% and 25.3%, respectively). This was primarily driven by an increase in cover of the grass Ammophila breviliuglata by 10-12% in N and NP plots compared to P and R plots. Our data shows that additions of nutrients can cause changes in community productivity and changes in species dominance. Here, an increase in dominance of C3 grass, A. breviligulata, in response to nutrient additions could alter community dynamics as this species is usually outcompeted by C4 species under the low nutrient conditions of barrier island swales.