Species turnover in nematode communities along an elevational gradient is driven by turnover in trophic groups and stochastic assembly processes

Background and aims: Nematodes play critical roles in mountain ecosystems, but their distribution patterns and community assembly remain poorly understood. This study aimed to clarify the distribution patterns and community assembly processes of soil nematode communities and their trophic groups along the elevation gradient on Changbai Mountain in northeast China, both for the whole mountain and for the north- and west-facing slopes. 

Methods: A total of 108 soil samples were collected from nine elevations (600–2,200 m a.s.l) for the north- and west-facing slopes of Changbai Mountain. We investigated the community similarity and assembly of whole nematode communities and within trophic groups, and assessed the relative contribution of elevation, environmental, and geographical distances to their spatial variations and community assembly processes. 

Results: Species turnover primarily accounted for the changes in nematode community composition along the elevation gradient, with communities shifting from plant-parasites dominating at lower elevations (600–1,000 m) to fungivores at mid-elevations (1,200–1,600 m) and omnivores-predators at higher elevations (1,800–2,200 m). Stochastic processes dominated the community assembly of whole nematode communities and within trophic groups across the whole mountain and on both north- and west-facing slopes, primarily as an undominated scenario where the influences of dispersal and selection were weak. Geographical distance emerged as the primary factor affecting both the community composition and assembly processes of whole nematode communities. However, the relative contribution of elevation, environmental and geographical distances exhibited different impacts on the community composition and assembly processes of each trophic group.

Conclusions: Overall, our findings underscore the importance of species turnover and stochastic processes in shaping and maintaining the composition of soil whole nematode communities and within trophic groups along the elevation gradient in Changbai Mountain.