Nutrient Supply Shapes Microbial Assembly in Dryland Biocrusts: Taxon-Specific Responses and Network Reorganization

Biological soil crusts (biocrusts) cover ~30% of global drylands and regulate biogeochemical cycles through microbial metabolic activities. Although nutrient scarcity profoundly influences biocrust microbial communities, the general principles governing their nutrient response dynamics remain unclear. Here, we employed controlled microcosms to investigate how differential nutrient supply reshaped the community structure and interspecies interactions of both biocrust bacterial and fungal assemblages. Our findings revealed that increased nutrient supply drove a shift from K- to r-strategists in bacterial communities, while fungal assemblages exhibited distinct response patterns among abundant, intermediate, and rare taxa. Network analysis demonstrated that nutrient supply increased node number, link number, average degree, and negative correlations, indicating intensified interactions in both bacterial and fungal communities. Keystone taxa analysis identified three oligotrophic bacteria, three copiotrophic bacteria, and two fungal hub taxa consistently present across nutrient levels. Furthermore, both bacterial and fungal community structures, as well as their interaction networks, were strongly correlated with soil nutrient availability, particularly total phosphorus, available nitrogen, and available potassium. This study establishes a unified mechanistic framework for nutrient-driven microbial assembly in drylands, highlighting taxon-specific responses and interactions. The findings provide actionable strategies for ecological restoration through optimized nutrient management and targeted manipulation of keystone microbial taxa.