Impact of Agricultural Practices on Bacterial Carbon Use Efficiency
Z. M. Lee and T. M. Schmidt
Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI

Soil organic carbon (SOC) is highly responsive to shifts in land management and climate, with conventional agricultural practices reducing SOC. While microbial activity contributes to the conversion of SOC to carbon dioxide, another component of microbial metabolism that is typically not considered is the efficiency with which microbes incorporate carbon into more refractory structural biomass. The flow of carbon from a more labile fraction (plant exudates and residues) to a more recalcitrant fraction is important in regards to carbon biosequestration and long-term sustainability. The ratio of carbon incorporated into biomass versus that respired to CO₂ is known as the carbon use efficiency (CUE). In SOC models such as CENTURY, the ratio is assumed to be 0.45 for all soil types and land use. However, the proportion of carbon incorporated into biomass can be influenced by factors intrinsic to the microbes and external factors such as nutrient availability and substrate quality. This study assesses the impact of agricultural land use on bacterial CUE by measuring bacterial productivity and bacterial respiration for soil from a conventional agriculture and a native site at the Kellogg Biological Station LTER site. Preliminary result indicates that bacterial CUE differs for soils under different land management, with the bacterial community from agriculture soil performing less efficiently in terms of carbon biosequestration than the community in native soils underlying a midsuccessional plant community. The goal of this study is to better understand the consequence of the decrease in bacterial CUE in terms of modeling SOC and to elucidate factors that regulate bacterial CUE in terrestrial ecosystems.