Response of soil nematode community structure, diversity, and ecological network to elevation gradients in wild fruit forest of Tianshan Mountain, China

Background The Tianshan wild fruit forest is a special deciduous broad-leaved forest located in the mountains of central Asia. Methods To reveal how the Tianshan wild fruit forest ecosystem responds to environmental changes along an elevation gradient, we used the soil nematode index, which is widely recognized as a key indicator of soil health. This study focused on the nematode communities beneath Juglans cathayensis and Malus sieversii , two typical constructive species in the Tianshan wild fruit forest. Six elevation levels (1,480, 1,401, 1,351, 1,305, 1,252, and 1,207 m) were selected, and a nematode co-occurrence network was constructed for each elevation. We analyzed the abundance, diversity, ecological indices, and network complexity of soil nematode communities across different elevation gradients. In addition, we explored the relationships among environmental factors, soil multifunctionality, and nematode community characteristics. Results Our results showed that: (1) a total of 60,795 nematodes, representing 80 genera were collected. Total abundance, trophic group abundance, and diversity of nematodes peaked at middle elevations. However, in M. sieversii , nematode diversity increased with elevation. (2) The soil food web in the wild fruit forest exhibited a relatively high metabolic rate (nematode channel ratio > 0.5). (3) In J. cathayensis , the nematode ecological network was more complex and tightly interconnected at low elevations. whereas in M. sieversii , greater network complexity was observed at high elevations. (4) Environmental factors (organic matter, pH, total phosphorus, available potassium, total potassium) significantly affected the composition of nematode trophic groups ( p < 0.05). Moreover, network complexity was a key factor influencing soil multifunctionality. This study provides a theoretical foundation for long-term monitoring of soil health in Tianshan wild fruit forest.