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Stoichiometric theory shapes enzyme kinetics in paddy bulk soil but not in rhizosphere soil

The available carbon (C) to phosphorus (P) ratio in the soil is regulated by extracellular hydrolases for C and P acquisition by microbes and plants. However, the stoichiometric relationship between acquiring C and P in paddy rhizosphere and bulk soils remains unclear. The objective was to explore the underlying mechanisms of C and P acquisition stoichiometry in rhizosphere and bulk soils in response to P fertilization and cellulose addition. Amendment with either cellulose or P separately caused a significant increase in the maximal velocity (Vmax) of C acquisition enzymes (β‐1,4‐glucosidase and β‐cellobiohydrolase) but decreased that of P acquisition enzymes (acid and alkaline phosphomonoesterases) in bulk soil. In contrast, lower Vmax values of C and P acquisition enzymes were observed in rhizosphere soil than in bulk soil. The co‐application of cellulose and P increased the Vmax of P acquisition enzymes in rhizosphere soil but decreased that of only alkaline phosphomonoesterase in bulk soil. Results show that P availability and labile‐C content co‐regulated the P/C acquisition ratio, and two inverse linear relationships were observed. Specifically, the P/C acquisition ratio was negatively related to both the dissolved organic C/Olsen‐P ratio and the microbial biomass C/P ratio in rhizosphere soil. However, the P/C acquisition ratio was positively related to both the dissolved organic C/Olsen‐P ratio and the microbial biomass C/P ratio in bulk soil. Overall, microbes mineralized less organic P to acquire P in paddy soil rhizosphere (i.e., containing higher labile‐C) than in bulk soil (i.e., having lower labile‐C contents).