Urbanization simplifies soil nematode communities and coincides with decreased ecosystem stability

Urbanization is threatening terrestrial biodiversity and ecosystem functions. Nematodes, as one of the most abundant animals on Earth, play diverse roles within soil food webs and contribute to vital ecosystem services. However, the effects of urbanization on soil nematode functional groups, and the ecological functions and services they provide remain poorly understood. Here, we investigated functional groups of soil nematodes across 12 cities in China and validated the results by using a global nematode dataset. Specifically, we found the proportions of omnivores (by 45 similar to 60%) and predators (by 40 similar to 50%) as well as temporal ecosystem stability (by 10 similar to 20%), as indicated by the normalized difference vegetation index, were reduced in urban ecosystems, while the proportions of fungivores and bacterivores increased (30-60% and 10-20%, respectively). We identified total soil phosphorus and nitrogen as the main drivers influencing soil nematode feeding groups in urban ecosystems. Soil pH, mean annual precipitation, and mean annual temperature were predominant factors in non-urban ecosystems. We further demonstrated that nematode functional guilds contributed to ecosystem stability in urban ecosystems, but this was not true in non-urban ecosystems. Our findings evidence the homogenization effects of urbanization on key functional guilds of soil nematodes and their roles in maintaining ecosystem stability. The fact that ecosystem stability and the abundance of nematode functional guilds are closely related and driven by climatic, edaphic, and anthropogenic factors may help in setting priorities for urban soil management.