C:N:P stoichiometry regulates soil organic carbon mineralization and concomitant shifts in microbial community composition in paddy soil

Stoichiometric control of input substrate (glucose) and native soil organic C (SOC) mineralization was assessed by performing a manipulation experiment based on N or P fertilization in paddy soil. Glucose mineralization increased with nutrient addition up to 11.6% with combined N and P application compared with that without nutrient addition. During 100 days of incubation, approximately 4.5% of SOC was mineralized and was stimulated by glucose addition. Glucose and SOC mineralization increased exponentially with dissolved organic C (DOC):NH4+-N, DOC:Olsen P, and microbial biomass (MB)C:MBN ratios. The relative abundances of Clostridia and beta-Proteobacteria (r-strategists) were increased with combined C and NP application at the beginning of the experiment, while the relative abundances of Acidobacteria (K-strategists) were enhanced with the exhaustion of available resource at the end of incubation. The bacteria abundance and diversity were negatively related to the DOC:NH4+-N and DOC:Olsen P, which had direct positive effects (+ 0.63) on SOC mineralization. Combined glucose and NP application decreased the network density of the bacterial community. Moreover, P addition significantly decreased the negative associations among bacterial taxa, which suggested that microbial competition for nutrients was alleviated. The relative abundances of keystone species showed significant positive correlations with SOC mineralization in the soils without P application, revealing that microbes increased their activity for mining of limited nutrients from soil organic matter. Hence, bacteria shifted their community composition and their interactions to acquire necessary elements by increasing SOC mineralization to maintain the microbial biomass C:N:P stoichiometric balance in response to changes in resource stoichiometry.