Fewer new species colonize at low frequency N addition in a temperate grassland

1. Biologically reactive nitrogen (Nr) enrichment threatens biodiversity in diverse ecosystems. Previous controlled N addition experiments may overestimate the effects of atmospheric Nr deposition on the rate of species loss, as it has been found that low frequency Nr additions, as used in traditional studies, lead to more rapid biodiversity loss. It remains unclear, however, whether the colonization of new species (gain) or extinction of old species (loss) is the cause of this difference. 2. By independently manipulating the frequency (twice vs. monthly additions yr–1) and the rate (from 0 to 50 g N m–2 yr–1) of NH4NO3 inputs for six years in a temperate grassland of northern China, we aimed to examine the contribution of gain and loss of species to the reduction in species richness under different regimes of Nr inputs. 3. Results showed that the gain of new species was higher at a high frequency of N addition than that at a low addition frequency, whilst loss of existing species was s...