Nitrogen Addition, Watering, and Mowing Alters Microbial Diversity and Network Complexity in a Poisonous Weedy Degraded Grassland

ABSTRACT Understanding the responses of soil biota to global changes is crucial for the maintenance of ecosystem functions. The impact of global changes on the diversity of soil microbial communities in severely degraded grassland ecosystems invaded by a single poisonous weed remains unclear. This study conducted a control experiment on degraded grasslands with Sophora alopecuroides as a single dominant species and examined soil microorganism response to nitrogen addition, watering, and mowing. Our results showed that: (1) Nitrogen addition, watering, mowing, nitrogen‐water interaction, and nitrogen‐mowing interaction significantly reduced soil bacterial diversity, while there were no significant effects on soil fungal diversity. Nitrogen, watering, mowing, and their interaction increased the proportion of fungi in the microbial co‐occurrence network. (2) Nitrogen addition, watering, and mowing significantly affected the bacterial and fungal community composition, and fungivores nematodes abundance had a significant effect on the abundance of fungi and bacteria dominant phyla. (3) Nitrogen addition had indirect effects on bacterial richness and diversity mainly through nitrate nitrogen and soil pH. The abundance of fungivores nematodes had direct and significant negative effects on bacterial diversity and fungal richness. The results revealed that fungivores nematodes are higher trophic level soil fauna that influence fungi and bacteria, but the mechanism was still unclear. Nitrogen addition, watering, and mowing affect the changes in microbial diversity and the stability of food webs by increasing soil nutrients, changing the aboveground poisonous weed structure, and affecting soil fauna, which can contribute new perspectives for the restoration of degraded grassland with severe invasion of poisonous weeds.