Figure 4 The effects of different trophic species diversity on ecosystem functions: (a) water conservation; (b) soil fertility; (c) nutrition cycling and transformation; (d) community productivity; (e) ecosystem multifunctionality. The solid lines indicate significant relationship and the dashed lines indicate no significant relationship.
3.4 Contribution of multitrophic species diversity in explaining ecosystem multifunctionality
Variation partitioning analysis was used to quantify the relative importance of biotic variables of multitrophic diversity (plant diversity, bacterial diversity, fungal diversity, and rodent diversity) and the abiotic variables of altitude and soil environment (pH). Multitrophic diversity and abiotic variables (pH and altitude) accounted for 35% and 27% of the variation in water conservation and soil fertility, respectively (Figures 5a and b). Compared with altitude and pH, multitrophic diversity accounted for a higher proportion to predict nutrition cycling and transformation, and community productivity (Figures 5c and d). More importantly, multitrophic diversity and altitude accounted for a similar proportion (26%) of the explained ecosystem multifunctionality (Figure 5e). The results suggested that multitrophic diversity and altitude were more important in supporting specific ecosystem functions. Accordingly, we constructed a Piecewise SEM which explained 76% of variation in ecosystem multifunctionality. Effects of biotic and abiotic variables on ecosystem multifunctionality followed two paths: first, pH and altitude had direct negative and positive effect on ecosystem multifunctionality respectively; Second, pH had an indirect positive influence on ecosystem multifunctionality via its negative effects on niche breath and multitrophic diversity. (Figure 6).