Soil nematode diversity depends on understory plant species richness in a subalpine forest

As model soil invertebrates, nematodes are the most numerous and functionally diverse multicellular animals in terrestrial ecosystems, having significant effects on plant productivity, soil food web, and organic matter decomposition. While abiotic influences on soil nematode diversity are well known, the effects of biological factors and their interactions remain unclear. Based on combined field surveys with high-throughput sequencing, this study evaluated the impacts of biotic and abiotic factors on soil nematode species richness, Shannon diversity and trophic diversity in a subalpine coniferous forest in Sichuan, China. The results showed that plant diversity and richness exerted a greater influence on the species richness (ranging from 12 to 61) and Shannon index (ranging from 1.0 to 3.5) of soil nematode than abiotic factors (elevation and soil properties). Compared with trees, the species richness and density of understory shrubs and herbs exhibited significant negative correlations with soil nematode diversity. Interestingly, the relative abundances of lower trophic groups were mediated by both plants and higher trophic groups, whereas a bottom-up effect was observed on predators. These findings highlight the vital role of understory shrubs and herbs in shaping the trophic structure and diversity of soil nematode communities in coniferous forests, suggesting that understory diversity should be incorporated into models of soil nematode food webs in forest ecosystems.