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.

生物土壤结皮（BSC）是沙漠生态系统的重要组成部分。BSC的发展丰富了养分，创造了生态位分化并推动了土壤微生物群的变化。然而，BSC的发展如何驱动土壤原核生物和真菌群落相似性的动力学，而群落组合仍然完全难以捉摸。在这里，我们评估了微生物分类学和系统发育相似性与BSC发育阶段的差异。结果表明，在BSC后期，原核生物群落趋于趋同，这主要是由营养物积累对环境的过滤所致。确定性过程和随机过程分别在原核和真菌群落中占主导地位。大多数原核生物专家（例如放线菌，在后期的BSC阶段，Proteobacteria和Thaumarcaeota）以及地衣真菌的通才更为丰富。一些原核生物通才（例如，类细菌，蓝细菌，变形杆菌）与扁平化真菌的通才可能存在共生（正）关系。BSC的发展促进了原核生物多才多艺的丰富，但通过提高初级生产力，原核生物专家和真菌多才多艺的专家减少了。此外，原核共现网络（Co-MENs）趋向于不那么复杂，联系也较少。总体而言，原核生物通才的增加，专家数量的减少以及复杂性较低的Co-MEN的支持都表明，在BSC后期，原核生物群落的融合程度更高。