Microbial biomass and ecoenzymatic stoichiometries vary in response to nutrient availability in an arable soil

To evaluate whether microbial stoichiometries of biomass and enzyme activity could vary in response to changes in nutrient availability in an arable soil during the crop growth period, temporal variation in nutrient availability, soil enzyme activities associated with carbon (C), nitrogen (N), phosphorus (P), and sulfur (S) acquisition, and microbial biomass C, N, and P were measured in an Allophanic Andosol amended with chemical fertilizer and cow manure. The ratio of l-asparaginase to β-d-glucosidase activities had a significant negative correlation with potentially mineralizable N. In addition, the ratio of arylsulfatase to β-d-glucosidase activities showed a significant negative correlation with available S. Thus, it seems plausible that microorganisms in the soil would allocate their resources to synthesis of N- and S-acquiring enzymes in response to variation in the nutrient availability caused by fertilization and over time. Also, the ratio of microbial biomass C/P had a significant negative correlation with available P, suggesting that this stoichiometry could reflect P availability in the soil. These results imply that microbial biomass and ecoenzymatic stoichiometries are useful for evaluating nutrient availability in soils.