Simulated nitrogen deposition and precipitation events alter microbial carbon cycling during early stages of litter decomposition

Abstract Plant litter decomposition is a major nutrient input to terrestrial ecosystems that is primarily driven by microorganisms. Litter decomposition results in a flow of dissolved organic carbon (DOC) that links above-ground decomposition to below-ground microbial processes. Litter decomposition is expected to be altered by human-induced global disturbances—specifically nitrogen deposition and altered intensity and frequency of precipitation events—but little is known about impacts on the mobile pool of DOC. This study investigated the effect of simulated nitrogen deposition and increased precipitation events on microbially-driven carbon flow during short-term litter decomposition using a ‘common garden’ experimental design with microcosms containing sterile sand and blue grama grass litter inoculated with different soil microbial communities. Respiration (CO2) was measured throughout the experiment while microbial biomass carbon and nitrogen were quantified at the end. Overall, nitrogen deposition decoupled CO2 and DOC during short-term litter decomposition with respiration increasing and no affect on DOC concentration. Moreover, nitrogen deposition increased microbial biomass and had no effect on carbon use efficiency (CUE). Simulated precipitation events significantly increased DOC concentrations, decreased CUE, increased the microbial metabolic quotient (qCO2), and greatly altered microbial composition and diversity. These findings highlight the complex interactions and responses of surface litter decomposers to the combined effects of climate change and supports the need for more research into how varying microbiomes will respond to different global change scenarios. Furthermore, this study clearly indicates that any increases in soil carbon sequestration from nitrogen deposition are unlikely to arise from a larger supply of DOC.