Sulfur deposition changed the community structure of soil nematodes by affecting omnivores-predators

Nematodes generally occupy multiple trophic levels in detrital food webs, which play a vital role in energy flow, material conversion and nematodes community structure stability in the underground ecosystem. Sulfur (S) is one of the important soil nutrients, and it plays an important role in the nutrient cycle of grassland ecosystem. However, the impacts of S on soil fauna and subsurface detrital food webs in grassland ecosystems were rarely studied. Accordingly, to investigate the effects of sulfur deposition on soil nematodes and detrital food webs, we conducted a S addition experiment with distinct intensities from 0 to 50 g S m^-2 yr^-1 (S 0, S 1, S 2, S 5, S 10, S 15, S 20, and S 50) to simulated sulfur deposition in a meadow steppe of northern China. We documented a significant effect of S addition on the diversity and richness of nematodes, and the species richness of soil nematodes was high in the study site. But S addition had no significant effect on the total abundance and dominant species of nematodes (Cervidellus and Aphelenchus). Results of correlation analysis and structural equation modeling consistently indicated that omnivores-predators were significantly affected by sulfur addition. A significant increase in the Structural Index (which indicates food web structure) suggested increased top-down forces and changed community structure, although bacterivores, fungivores, plant parasites did not significantly. The present results suggest that sulfur deposition would change the composition of nematode community, affect the stability of nematode community structure, and increase the disturbance to the underground ecosystem. The study provides that the detailed information of the response of nematode to S deposition can be used to analyze the process of global change affecting the underground ecosystem.