Fig. 3 Compositions of microbial communities along anthropogenic disturbance gradients in the river ecosystems of Qinling Mountains. Non-metric multidimensional scaling (NMDS) ordination based on Bray-Curtis dissimilarity showing microbial community variation in water (a: autumn, b: spring) and sediment (c: autumn, d: spring) samples under different land-use types.
We used Mantel’s test to determine the impacts of environmental factors and land-use types on microbial community composition in the study area. NH4+-N, Cond, T, TN, and NO3--N showed significant correlations (P < 0.01, Mantel’s r> 0.1) with microbial community composition in water. N and P contents increased with an increase in the proportion of agricultural land; however, both elements tended to decrease with an increase in the proportion of forest land, which further affected microbial community composition. In addition, the proportions of agricultural land, forest, and grassland areas were significantly correlated (Mantel’s r> 0.2, P < 0.01) with sediment microbial community composition (Fig. 4). Based on results of microbiota community composition analyses in river water and sediment over the two seasons, different land-use types had considerable impacts on microbial community composition in river water and sediment (Fig. S5a-b).