Ecoenzymatic stoichiometry reveals the exacerbation of microbial C and N limitations by moss crusts in degraded karst ecosystems

Soil microorganisms are susceptible to changes in soil environments, particularly nutrient deficiencies, and respond to nutrient limitations by adjusting the production of extracellular enzymes. Biological soil crusts (BSCs) serve as a medium for surface soil microorganisms and nutrient cycling, significantly affecting soil and microbial characteristics. However, research on the effect of BSCs on soil microbial nutrient limitations is scarce in degraded karst ecosystems. This study focused on moss crusts in four karst ecosystems with varying degrees of degradation, using bare soil as a control. We collected and measured the physicochemical properties and enzyme activities of surface soil, quantified microbial nutrient limitations, and explored significant factors affecting these limitations. Results showed that microbial carbon (C) and nitrogen (N) limitations were prevalent in degraded karst ecosystems (vector length, VL > 0.61, vector angle, VA < 55°), with C limitation intensifying as degradation degrees increased, while N limitation showed a unimodal trend. The presence of moss crusts increased C- (β-1,4-glucosidase, BG) and N- (β-1,4-N-acetyl-glucosaminidase, NAG, leucine aminopeptidase, LAP) acquiring enzyme activities, and overall exacerbating microbial C and N limitations (p < 0.05). Available potassium (AK), soil organic carbon (SOC), pH, and total nitrogen (TN) were the most influential factors in microbial nutrient limitations (p < 0.05). This study enhances our understanding of soil nutrient conditions, microbial characteristics, and the ecological functions of moss crusts in degraded karst ecosystems, improving knowledge of biogeochemical cycles of nutrients in plant-soil-microbe systems and offering new insights into deeper studies of soil microbial nutrient limitations.