Different facets of bacterial and fungal communities drive soil multifunctionality in grasslands spanning a 3,500 km transect

1. Soil microbial communities are essential in
regulating ecosystem functions and services. However, the importance of
bacterial and fungal communities as predictors of multiple soil
functions (i.e., soil multifunctionality) in grassland
ecosystems has not been studied systematically.
2. Here, we measured soil microbial diversity,
community composition, biomass, and multiple soil functions of 41 sites in
five grassland ecosystems spanning a 3,500 km
northeast–southwest transect. The random forest algorithm was
adopted to determine the importance of geographical
location, climatic, altitude, edaphic, plant, and
microbial predictors in driving a proxy of soil
multifunctionality (seven soil functions in this study).
Moreover, structural equation models (SEMs)
were employed to examine the direct and indirect effects of those
predictors on soil multifunctionality. 3. Our results
demonstrated that soil multifunctionality was positively driven by soil
fungal diversity but not by bacterial diversity. Fungal phylogenetic
diversity (presence of different evolutionary lineages) showed stronger
positive relationships with soil multifunctionality than
taxonomic diversity (richness of species). Dominant
bacterial taxa, particularly of phyla Actinobacteria and
Proteobacteria, were positively associated with soil multifunctionality,
while none of the fungal taxa were found to regulate
soil multifunctionality. Furthermore, both fungal and bacterial
biomass had significant effects on soil
multifunctionality, while the effect of microbial biomass was weaker than
that of fungal diversity and bacterial taxa. Importantly, the direct
positive effects of soil fungal diversity, dominant bacterial
taxa, and fungal and bacterial biomass were maintained after
accounting for multiple predictors in grassland ecosystems.
4. This study provided strong empirical evidence that soil
multifunctionality was driven by different facets of the
bacterial and fungal communities in the grassland
ecosystems. Our results also highlighted that
any loss of fungal diversity, dominant bacterial
taxa and microbial biomass might reduce soil
multifunctionality, exacerbating ecosystem functions and
services such as soil fertility, primary production, and
climate mitigation in grassland ecosystems.