Global nitrogen (N) fertilizer production and consumption are expected to further increase in the coming years. Consequently, it may yield an increase in atmospheric N deposition in the following decades worldwide. Nitrogen enrichment through either fertilization or atmospheric deposition is known to alter the stability of ecological communities. However, we know little about how N enrichment affects community stability across spatial scales. We conducted a field N addition experiment with 19 treatments in a temperate grassland. Nine rates (0, 1, 2, 3, 5, 10, 15, 20, and 50 g N m–2 year–1) crossed with two frequencies (2 times year–1 vs. monthly) of N addition were manipulated with purified NH4NO3. Aboveground biomass and species richness were recorded every year from 2009–2013 between 10 and 15 August using a 0.5m × 2m quadrat, which was randomly placed in each 8-m × 8-m experimental plot. We treated the 0.5m × 2m quadrat (i.e., 1-m2) and the sum of the 10 replicated quadrats (i.e., 10-m2) as local and large scales, respectively.
Results/Conclusions
We found that although both plant species richness and community biomass temporal stability increased with spatial scale, N enrichment reduced richness and stability at both scales considered. Reduced alpha stability (i.e., the community stability at the 1-m2 scale) under N enrichment arose from N-induced reduction in population stability, which was partly driven by the decline in species richness, and reduction in asynchronous dynamics across species. Gamma stability (i.e., the community stability at the 10-m2 scale) was strongly influenced by alpha stability, but its decline under N enrichment was buffered by spatial asynchrony among local communities, which was unaffected by N enrichment. These results suggest that conserving local diversity and spatial heterogeneity among local communities may alleviate the adverse impacts of anthropogenic environmental changes on ecosystem dynamics at larger spatial scales.