Plant and microbial β diversities are better predictors of ecosystem functioning than their α diversities, but aridity weakens these associations

Understanding the linkage between community heterogeneity (β diversity) and ecosystem functioning is crucial for uncovering complex ecological processes that impact ecosystem stability and productivity. However, our understanding of how β diversity is associated with ecosystem functioning across environmental gradients remains limited.

We conducted an aridity-gradient transect survey of grassland over 3500 km across the Tibetan Plateau (a total of 80 grassland sites) to investigate the changes of plant and soil microbial diversities along a natural aridity gradient, and to evaluate the above- and belowground biomass and plant nutrient levels connected with the observed variation.

Our results showed that plant richness, above- and belowground biomass, plant nutrient concentrations, and soil microbial α and β diversities (including taxonomic and functional) significantly decreased along the aridity gradient. Compared to the α diversities of plant and microbial community, their β diversities were more significantly correlated with above- and belowground biomass and plant carbon, nitrogen and phosphorus concentrations. Metagenomic functional profiles showed that β diversity of microbial functions, including genes of the carbohydrate metabolism responsible for carbon degradation, nitrification, energy production and conversion, material transport and coenzyme metabolism, had closer associations with plant biomass and nutrient concentrations than did their α diversities. These positive β biodiversity-functions association was weakened by the increasing aridity, mainly because the increasing aridity-induced lower biomass of plant functional groups (e.g., sedge and forbs), soil moisture and organic carbon content decreased both plant and soil microbial β diversities.

These findings provide novel insight into the biodiversity-ecosystem functions relationship and stress the crucial roles of above- and belowground β diversity in supporting alpine grassland biomass and nutrient levels. Biodiversity conservation to prevent large-scale community homogenization should be attached in alpine ecosystem.