Effects of short-term nitrogen addition, watering, and mowing on soil nematode community in poisonous weed type degraded grasslands

Global changes in nitrogen deposition, precipitation patterns and land use could have an impact on soil biotas. Soil nematodes are important indicators of ecosystem function in degraded grasslands, and how global climate change affect soil nematode communities in degraded grasslands with poisonous weeds needs further study. This study conducted a control experiment on degraded grasslands with Sophora alopecuroides as a single dominant species. We set up a total of eight treatments, which are no nitrogen, no watering, no mowing (CK), nitrogen addition (N treatment), watering (W treatment), mowing (M treatment), nitrogen × watering (NW treatment), nitrogen × mowing (NM treatment), watering × mowing (WM treatment), nitrogen × watering × mowing (NWM treatment). We analyzed the patterns of change in nematode abundance, richness, ecological indices, and co-occurrence networks, as well as the relationships among nematode trophic taxa, soil salinity, and plants. Our results showed that: (1) Paratylenchus and Acrobeles were the main dominant genera. NW treatment significantly increased the relative abundance of plant parasites and significantly decreased the relative abundance of bacterivores. (2) N and NWM treatments increased nematode community network complexity. W, M, and WM treatments decreased nematode community network complexity. (3) Plant Parasites and Bacterivores nematodes community composition were significantly correlated with the structural characteristics of S. alopecuroides (biomass, height, coverage; biomass, height). Fungivores nematodes and Omnivores/Predators nematodes community composition were significantly correlated with soil salinity ions (Cl^-, Mg²⁺; SO₄^2-). (4) The average degree (characterizing the interaction intensity among nematodes genera and sparsity-density of the nematode ecological network) was significantly positively correlated with soil multifunctionality. In addition, the interaction of nitrogen and watering addition on the abundance of different feeding nematodes than nitrogen and watering addition alone. Mowing can alleviate the negative effects of nitrogen addition and watering on soil food webs. Our study suggested that there are complex interactions between soil nematodes and environmental factors in grassland ecosystems, and provided new insights for understanding the impact of global change on the formation and change of soil fauna diversity in poisonous weed type degraded grasslands.