Relative importance of altitude shifts with plant and microbial diversity to soil multifunctionality in grasslands of north-western China

Background and aims Above- and belowground biodiversity determines the capacity of ecosystems to provide multiple functions simultaneously (i.e., multifunctionality), while their relative importance along environmental gradients remains unclear. Our objective of this study was to investigate how plant and microbial diversity along an altitudinal gradient affected soil multifunctionality in grasslands. Methods The effects of plant and microbial (including bacteria, fungi and archaea) diversity on soil multifunctionality were estimated along a 2300 m altitudinal gradient across six grassland types in the Tianshan Mountain, China. The soil multifunctionality was calculated based on 12 parameters related to carbon, nitrogen, phosphorous cycling, and soil nutrient status. Results The relative importance of plant and microbial diversity to soil multifunctionality shifted at an altitude of 1900 m while threshold for each soil function varied along altitudinal gradient. At low altitudes (< 1900 m), plant species richness showed a robust positive effect and had a more substantial impact on soil multifunctionality than microbial diversity. Altitude had a significant effect on plant species richness via indirect means by altering soil moisture. At high altitudes (> 1900 m), soil multifunctionality was influenced by a combination of plant and microbial diversity. Similarly, fungal richness was positively associated with soil multifunctionality, while archaeal richness had the opposite effect. Conclusion The effect of plant and soil microbial diversity on soil multifunctionality was mediated by altitude in grasslands, which can guide the restoration efforts aimed to maximize soil multifunctionality in grassland ecosystems.