Distribution Patterns and Community Assembly of Soil Nematodes Along Elevation Gradients in a Dry-Hot Valley

In arid regions, mountain ecosystems are biodiversity hotspots but also highly fragile. While aboveground communities have been well studied, belowground communities-particularly soil fauna-remain poorly understood despite their key roles in ecosystem functioning. Soil nematodes play an important role in soil faunal communities. Here, we characterized soil nematode communities and soil properties in plots located at four different elevations in the Yuanjiang dry-hot valley, China. We examined the effects of soil properties on nematode abundance, diversity, and community composition, and explored the community assembly along the elevational gradient. Our findings suggest that the increase in soil moisture is the primary driver of the elevational rise in nematode abundance, but it is not the main factor responsible for changes in nematode diversity. Instead, with increasing elevation, NH₄ ⁺-N simultaneously promoted the abundance and diversity of plant parasites nematodes while reducing the diversity of bacterivores nematodes. We also found that NH₄ ⁺-N and MBC exerted stronger influences on nematode community composition than soil moisture, underscoring the importance of nutrient-related factors in shaping belowground biodiversity. Furthermore, soil moisture does not influence soil nematode community assembly as an environmental filter, but rather indirectly affects community assembly by regulating nematode abundance, suggesting that nematode communities in this arid region are adapted to low-moisture conditions. Our study provides new insights into the elevational distribution patterns of soil nematodes in arid mountain ecosystems and helps to fill a critical knowledge gap regarding nematode community assembly in arid environments.