Microbial community composition and interactions in saline biocrusts: Insights into cyanobacterial inoculation for soil restoration

Biocrusts play a pivotal role in maintaining ecosystem functions in arid and semi-arid saline environments. While inoculated cyanobacteria have been extensively studied for their contribution to biocrust development, the effects of high salinity on the composition and metabolic functions of cyanobacterial communities remain underexplored. In this study, we investigated the microbial community structure and interactions of biocrusts at three characteristic sites along a natural salinity gradient in the eastern Qubqi Desert, aiming to characterize microbial salinity preferences, particularly those of cyanobacteria, with a view toward informing inoculation strategies for saline soil restoration. Our findings demonstrate that although increased salinity reduced microbial diversity, microbial taxa exhibit varying responses to salinity, with Actinobacteria and Bacteroidota increasing in abundance at higher salinity levels, indicating their strong salt tolerance. While the whole nitrogen-fixing cyanobacteria were progressively replaced by other bacterial taxa, such as Pseudomonadota, in more saline environments, Scytonema, a nitrogen-fixing cyanobacterial genus, was found across all soil types, highlighting its adaptability to varying salinity levels. Additionally, the cyanobacterial genera Microcoleus and Oscillatoria showed notable resilience and growth in saline conditions, while new, unidentified cyanobacterial species emerged in high-salinity sites. Network analysis further revealed that increasing salinity led to greater complexity in microbial interactions, suggesting enhanced cooperative relationships within the microbial communities. These results underscore the significant role of environmental salinity in shaping microbial community structure and interactions, and highlight the potential of utilizing salt-tolerant cyanobacteria, in conjunction with other bacteria (e.g., nitrogen-fixing Pseudomonadota), for biocrust-based soil restoration in saline ecosystems, providing valuable insights for developing effective microbial inoculation strategies to rehabilitate saline soils.