Aridity mediates biocrusts' effects on soil multifunctionality in northern China

1. Soil biocrusts, as the fundamental component of drylands, alter soil
microbial and plant community compositions, thus profoundly affecting soil
multifunctionality (SMF). Biocrust development regulates microbial
composition and eco-physiological effects, but there have been limited
assessments regarding how biocrust development impacts SMF through
microbial communities and plant species. 2. We investigated the geographic
patterns of plant diversity, soil bacterial diversity, biocrust
development, and SMF along an aridity gradient, spanning 2,200 km in
northern China, and evaluated how biocrust development modulated multiple
soil functions related to carbon, nitrogen, and phosphorus cycles. 3.
Plant species richness and SMF decreased linearly with increasing aridity
(1-AI), but the relationship of soil bacterial diversity and biocrust
development index (BSCDI) with aridity differed between arid region and
semi-arid region. 4. Plant diversity and soil bacterial diversity
increased linearly with BSCDI in arid regions, but decreased linearly with
BSCDI in semi-arid regions. 5. Both plant species and soil bacterial
diversity exerted positive effects on SMF in arid regions, but soil
bacterial diversity, rather than plant species, did not explain any
variation in SMF in semi-arid regions. Most importantly, biocrust
development exerted direct effects on SMF in arid regions, but only
indirect effects through changing soil microbial biomass carbon in
semi-arid regions. 6. Our findings suggest that the effects and
influencing pathways of biocrusts on SMF are different between arid and
semi-arid regions, these results give a comprehensive view of how biocrust
development facilitates soil multifunctionality improvement and ultimately
promote a deeper understanding of the dependence of biodiversity-SMF
relationship on aridity.