The impact of slope position on the relationship between biodiversity and ecosystem multifunctionality in the Qinghai‐Tibet Plateau subalpine meadows

Abstract Plant and soil microbial communities are crucial in regulating various ecosystem functions. However, the specific effects of aboveground plant communities versus belowground microbial communities (e.g., protozoa, bacteria, and fungi) and their interactions on ecosystem multifunctionality (EMF) mediated by slope positions remain largely unknown. Here, we investigated the relationship between EMF and biodiversity indices on the upper, middle, and lower slopes of subalpine meadows on the Qinghai‐Tibet Plateau and how changes in plant and soil biodiversity and other abiotic factors mediate EMF. The results showed that plant diversity (species, function, phylogeny) and soil microbial diversity (bacteria, ciliates) were significantly higher on the downslope site than on the upper slope site, and EMF was significantly higher with decreasing slope position. Phylogenetic diversity and ciliate diversity were the dimensions of plant and soil biodiversity, respectively, that contributed most to EMF, suggesting the critical role of ecological niche complementarity and protozoan‐driven nutrient cycling in maintaining multifunctionality. Slope position alters the relationship between biodiversity and EMF by regulating resource allocation: soil biodiversity dominates EMF when relative slope position (RSP, i.e., the ratio of the relative elevation of the watershed) is <0.30; the role of plant diversity is enhanced when RSP is >0.34. Generally speaking, our study provides valuable insights into the critical role of multi‐trophic biodiversity in conserving ecosystem multifunctionality in subalpine grassland communities, as well as strong support for the importance of biodiversity conservation.