Increase in rainfall intensity promotes soil nematode diversity but offset by nitrogen addition in a temperate grassland.

Precipitation regime in arid and semi-arid regions is exhibiting a trend of increase in rainfall intensity but reduction in frequency under global climate change. In addition, nitrogen (N) deposition occurs simultaneously in the same regions. Nematodes are the dominant soil biota in terrestrial ecosystems and are involved in various underground processes. How the diversity of nematode communities responds to changing precipitation regime and how N deposition regulates the responses remain unclear. Here, we performed a field experiment initiated in 2012 to examine the effect of changes in the precipitation regime (2 mm precipitation intensity, 5 mm precipitation intensity, 10 mm precipitation intensity, 20 mm precipitation intensity, and 40 mm precipitation intensity) and N addition (10 g N m-2 yr-1) on soil nematode community in a semi-arid grassland in Inner Mongolia of China. We found that the abundance and diversity of nematodes increased under the treatments with fewer but stronger precipitation events (the largest abundance of total nematodes was 1458.37 individuals/100 g dry soil occurred under 40 mm intensity treatment). However, N addition reduced nematode diversity under these treatments, which largely offset the positive effects of increased rainfall intensity alone. Soil pH and plant belowground biomass were the main factors affecting nematode diversity. Our results imply that, as a consequence of global climate change, an increase in the intensity of rainfall events in the coming decades may favor the nematode communities within arid and semi-arid ecosystems. However, this positive effect may be largely offset by soil acidification in the regions experiencing heavy N deposition.