Increasing relative abundance of non-cyanobacterial photosynthetic organisms drives ecosystem multifunctionality during the succession of biological soil crusts

Biological soil crusts (biocrusts) are essential for ecosystem functioning, especially in drylands. However, we lack the knowledge of how ecosystem multifunctionality (EMF) responds to the development of biocrusts and the key factors mediating EMF during biocrust succession. In this study, we tested a series of essential ecosystem functions of the biocrust system and calculated a weighted EMF index, a processes-based EMF_processes index, and a resource storage and availability based EMF_pools index. Sequencing of the 16S rRNA gene and ITS gene was used to test differences in the community compositions of 16S rRNA gene-based organisms and ITS gene-based fungi in different biocrust stages. Results showed that the changing patterns and driving factors of all the three multifunctionality indices were similar. Later developed biocrust stages exhibited higher values of all three EMF indices. The 16S rRNA gene-based diversity reduced with biocrust succession. Biodiversity-EMF relationships varied when considering different biocrust stages and organisms. Across all biocrust stages, significantly negative relationships existed between the EMF indices and 16S rRNA based α-diversity, whereas positive relationships occurred between the EMF indices and both 16S rRNA and ITS gene-based β-diversity. Further analyses indicated that the increasing relative abundance of non-cyanobacterial photosynthetic organisms (represented by chloroplast sequences and lichenized fungi) was the key predictor of all three EMF indices during biocrust succession. Specifically, these organisms were Streptophyta, Chlorophyta and Bacillariophyta and lichenized fungi, e.g., Verrucaria, Caloplaca and Aspicilia. This study provided a mechanistic understanding of how biological compositions and diversity drive EMF with biocrust development.