Development of biological soil crust prompts convergent succession of prokaryotic communities

Biological soil crusts (BSCs) are vital components of desert ecosystems. Developments of BSCs enrich nutrients, create niche differentiation and drive the variations of soil microbiota. However, how BSC developments drive the dynamics of soil prokaryotic and fungal community similarities and community assemblages remain fully elusive. Here, we evaluated the variations of microbial taxonomic and phylogenetic similarities with the developmental stages of BSC. Results showed that prokaryotic communities tended to be convergent in later BSC stages, mainly driven by the environmental filtering through nutrient accumulation. Deterministic processes and stochastic processes dominated in prokaryotic and fungal community assemblages, respectively. Most prokaryotic generalists (e.g., Actinobacteria, Proteobacteria and Thaumarcaeota) and generalists of lichenized fungi were more abundant in later BSC stages. Some prokaryotic generalists (e.g., Bacteroids, Cyanobacteria, Deltaproteobacteria) showed possible symbiotic (positive) relationships with generalists of lichenized fungi. BSC development promoted the abundances of prokaryotic generalists, but reduced prokaryotic specialists and both fungal generalists and specialists through increasing primary productivity. Additionally, prokaryotic co-occurrence networks (Co-MENs) tended to be less complex and less connected. Overall, the increases of prokaryotic generalists and decreases of specialists and less complex Co-MENs supported that prokaryotic communities were more convergent in later BSC stages. Our results provided mechanistic understandings of the interactions among microbial community succession, niche specialization and BSC development.