Nutrient supply drives concurrent K-to-r strategist shifts and competitive intensification in biocrust bacterial communities

Biological soil crusts (biocrusts) cover ~30% of global drylands and regulate biogeochemical cycles through bacterial metabolic activities. Although nutrient scarcity profoundly influences biocrust bacterial communities, the general principles governing their nutrient response dynamics remain unclear. Here, we employed controlled microcosms to investigate how differential nutrient supply reshaped bacterial life-history traits and interspecies interactions in both cyanobacteria- and moss-dominated biocrusts. Our findings revealed that with increased nutrient supply, the ribosomal RNA gene operon (rrn) copy numbers in bacterial communities significantly increased, while the ratio of oligotrophs to copiotrophs decreased, indicating a shift from K-strategists to r-strategists. Network analysis showed that nutrient supply increased node number, link number, average degree, and negative correlations, indicating stronger interactions within the bacterial community. Keystone taxa analysis identified six keystone taxa, with Arthrobacter, Nocardioides, and Ellin6055 responding negatively, and Bacillus, Tumebacillus, and Fictibacillus responding positively to nutrient supply. Furthermore, bacterial community structure, including life-history strategies, network topology, and keystone taxa, was strongly correlated with soil properties, particularly the contents of available nitrogen and potassium and total phosphorus. Our study establishes a mechanistic framework for nutrient-driven bacterial assembly in dryland ecosystems, providing practical strategies for ecological stabilization through optimized nutrient management and targeted manipulation of bacterial keystone taxa.