N-induced biodiversity loss will persist with upscaling as β diversity decreased by N

Background/Question/Methods:

Many empirical studies show that anthropogenic N enrichment is an important threat to biodiversity. However, these conclusions are almost based on individual plots, it’s unclear how N affects biodiversity at larger scales, which is important to biodiversity management. In a 11 year-long N addition experiment with six levels of N addition rate, we investigated species richness of 1 m × 1 m quadrats arrayed in a contiguous grid, to construct the species-area relationships for each 5 m × 5 m experimental plots.

Results/Conclusions:

Our findings on a Inner Mongolia grassland demonstrated that (i) N addition had slightly increase the z-value from 0.269 (control) to 0.274 at low levels of additional N (1.75 g N m^-2 yr^-1) and 0.290 at high N rate (10.5 g N m^-2 yr^-1), but the difference was insignificant (p > 0.10), while c-value was significantly decreased by N addition; (ii) spatial scale (sampling size 1 m² – 25 m²) had no significant effect on species richness (SR) response ratio [Ln(SR_treatment/SR_control)]; (iii) N addition had decreased β diversity and the slopes of species abundance distribution curve (SAD), and the N effects were increased with experiment duration. Our results clearly indicate that N induced species loss will persist at larger scales as β diversity decreased. Since N has decreased the species pool, management that help the establishment of lost species will be important to maintain biodiversity.