Environmental controls on soil nematode composition and network complexity across a restoration chronosequence in a...

Soil nematodes are widely used indicators of soil ecosystem condition. However, their responses to ecological restoration are often assessed solely through diversity metrics, which may overlook important changes in community organization and species interactions. Here, we examined how soil nematode community composition, α-diversity, and co-occurrence network complexity responded to a mining restoration chronosequence in an alpine grassland on the Qinghai-Tibet Plateau, encompassing short-term restoration, long-term restoration, and native vegetation. Across restoration stages, nematode α-diversity indices (Shannon, Chao1, and Pielou's evenness) showed no significant differences, whereas community composition and trophic structure shifted markedly, particularly in the relative abundances of bacterivorous and predatory nematodes. In contrast to the stability of α-diversity, co-occurrence network complexity varied substantially, with long-term restoration sites exhibiting higher connectivity, clustering coefficient, and interaction density than short-term restoration and native vegetation. Environmental analyses revealed that soil properties explained the largest proportion of variation in community composition. Soil pH and phosphorus availability emerged as key predictors of both community composition and network complexity. Path modeling further indicated that chromium exerted strong indirect effects by regulating soil physicochemical conditions and plant belowground biomass, thereby influencing both community composition and network topology. Overall, our findings demonstrate that α-diversity alone provides limited sensitivity for detecting ecological recovery, whereas network structural attributes capture environmentally driven reorganization of belowground communities. Integrating nematode network analysis with environmental modeling offers a more sensitive framework for evaluating soil health and restoration outcomes in mining-disturbed alpine ecosystems.