Nitrogen and phosphorus additions interactively affected composition and carbon budget of soil nematode community in a temperate steppe

Soil nematodes play a fundamental role in regulating ecosystem carbon and nutrient cycling. It is widely recognized that soil nematode community composition is sensitive to nutrient enrichment, but the linkage between community assembly processes and functional changes under nutrient enrichment condition remains poorly understood. We examined the compositional and functional responses and quantified the role of main community assembly processes (genus losses, genus gains, and context-dependent variations of abundance) in driving the carbon budget of soil nematode communities in response to nitrogen (N) and phosphorus (P) addition in a temperate grassland. Nitrogen and P addition significantly interacted to affect nematodes abundance, biomass, and functional variables of C cycling, in that P addition increased all the variables under ambient N condition but not under N enriched condition. Soil pH, ammonium concentration, and total phosphorus concentration played important roles in driving the variations of nematode C budgets, indicating the minor role of plant community characteristics. The enhancement of all variables following P addition was caused by the increases in the abundance of common genera (e.g. Acrobeles, Scutylenchus, and Tylencholaimus). The variation of genus richness contributed to the P-induced increases of nematode abundance but not to the increases of carbon budgets. Our results uncover the linkages between community assembly processes and the abundance and C cycling function of soil nematode community under nutrient enrichment conditions. The significant interactive effects between N and P addition highlight the complexity in predicting the compositional and functional changes in soil nematode community under a scenario of multiple-nutrient enrichment.