ALBERT

Description: Ecological stoichiometry provides a powerful tool for integrating microbial biomass stoichiometry with ecosystem processes, opening far-reaching possibilities for linking microbial dynamics to soil carbon (C) metabolism in response to agricultural nutrient management. Despite its importance to crop yield, the role of phosphorus (P) with respect to ecological stoichiometry and soil C sequestration in paddy fields remains poorly understood, which limits our ability to predict nutrient-related soil C cycling. Here, we collected soil samples from a paddy field experiment after 7 years of superphosphate application along a gradient of 0, 30, 60, 90 (P-0 through P-90, respectively) kg P ha-1 y-1 in order to evaluate the role of exogenous P on soil C sequestration through regulating microbial stoichiometry. P fertilization increased soil total organic C and labile organic C by 1-14% and 4-96%, respectively, while rice yield is a function of the activities of soil ?-1, 4-glucosidase (BG), acid phosphatase (AP) and the level of available soil P through a stepwise linear regression model. P input induced C limitation as reflected by decreases in the ratios of C:P in soil and microbial biomass. An ecoenzymatic ratio indicating microbial investment in C versus P acquisition, i.e., ln(BG):ln(AP), changed the ecological function of microbial C acquisition and was stoichiometrically related to P input. This mechanism drove a shift in soil resource availability by increasing bacterial community richness and diversity, and stimulated soil C sequestration in the paddy field by enhancing C degradation-related bacteria for the breakdown of plant-derived carbon sources. Therefore, the decline in the C:P stoichiometric ratio of soil microorganism biomass under P input was beneficial for soil C sequestration, which offered a "win-win" relationship for the maximum balance point between C sequestration and P availability for rice production in the face of climate change. # doi:10.1890/14-0189.1