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.