Biocrust diversity enhances dryland saline soil multifunctionality

Biocrusts are multifaceted communities including mosses, lichens, and cyanobacteria that are crucial for sustaining soil functions in drylands. Most studies on biocrust functions to date have focused on biocrust cover and development, largely in non-saline soils, and we know very little about the importance of biocrust diversity for maintaining multifunctionality in saline dryland soils. We assessed the direct and indirect linkages between biocrust richness, soil texture and salinity and soil multifunctionality by measuring 13 variables characterizing soil biological, nutrient and hydrological functions across 32 plots in a salinized dryland in northeastern Iran. We assessed the species richness of biocrust patches and characterized soil functions in bare soils. Overall, biocrust species richness declined with soil clay content and soil salinity, whereas soil salinity increased with soil clay content. Structural equation modeling showed a strong positive association between biocrust species richness and all measured dryland soil functions (soil biological, nutrient, and hydrological functions), but soil hydrological function declined with soil salinity. Overall, dryland soil multifunctionality was positively associated with biocrust species richness but negatively associated with soil clay content. Biocrust species richness likely enhances soil multifunctionality via the distinct roles of species and biocrust functional groups in providing carbon and nutrient inputs, creating favourable microsites, enhancing infiltration, and facilitating soil microbial colonization in saline dryland soils. Overall, our findings highlight a key role for biocrust diversity in facilitating and maintaining soil multifunctionality in drylands affected by soil salinity.