Coupled Carbon and Nitrogen Inputs Increase Microbial Biomass and Activity in Prairie Bioenergy Systems

Soil microorganisms drive cycling and storage of soil carbon (C) and nitrogen (N) through decomposition of plant root and litter inputs. However, microbial activities vary greatly in time and space as well as with land management. The goal of this study was to address the seasonal role of microbial activity in soil C and N storage and cycling in harvested prairie and corn ecosystems. We measured extracellular enzyme activity, microbial biomass, extractable soil C and N, and total soil C and N at monthly intervals across two growing seasons in fertilized and unfertilized planted tallgrass prairie and compared them with a continuous Zea mays (corn) row-crop agroecosystem. Prairie systems supported greater microbial biomass and enzyme activity compared with corn systems; fertilized prairie systems had greater microbial activity than unfertilized prairies. The magnitude, and in some cases direction, of differences in response variables among the three managed systems changed seasonally. Overall, microbial biomass and enzyme activity were stimulated by increased C inputs (roots) in prairies and were further enhanced with N additions in fertilized prairies. Furthermore, seasonal fluctuation in microbial activity underscores the importance of considering when soils are sampled to estimate and predict patterns in microbially driven C and N cycling at the ecosystem level.