Soil water content drives the spatiotemporal the distribution and community assembly of soil ciliates in the Nianchu River Basin, Qinghai-Tibet Plateau, China

Ciliated protozoa (ciliates) are an ecologically important group of microeukaryotes that play roles in the flow of energy and nutrients in aquatic and terrestrial ecosystems. The community distribution and diversity of soil ciliates in the Nianchu River Basin were investigated by sampling four major habitats, i.e., grassland, farmland, wetland and sea buckthorn forest during May, August and October 2020. Cultivation identification and enumeration of soil ciliates were performed by the non-submerged culture method, in vivo observations and protargol silver staining, and direct counting methods, respectively. A total of 199 species were identified representing, 89 genera, 67 families, 31 orders and 11 classes. Haptorida was the dominant group with 35 species, accounting for 17.59% of the total. The results showed that the alpha and beta diversity indices of soil ciliate communities in the Nianchu River Basin varied significantly in spatial distribution, but not in temporal distribution. Mantel test showed that soil water content, total nitrogen and organic matter were significantly correlated with soil ciliates. Soil water content was the main environmental factor driving the spatial distribution of soil ciliates. Co-occurrence network analysis showed that soil ciliate species in the Nianchu River Basin depend on each other in the relationship of solidarity and cooperation or ecological complementarity. Thus maintaining or enhancing the diversity and stability of the community. Community assembly shows that randomness process was an important ecological process driving soil ciliate community construction in the Nianchu River Basin.