Unintended Consequences of Biofuel Feedstock Production On Carbon and Nitrogen Cycle Dynamics Mediated by Soil Biology.

Increased interest in the utilization of plant biomass for the production of cellulosic ethanol raises concern for the potential of unintended environmental consequences related to soil carbon (C) and nitrogen (N) cycling. Our hypothesis is that different biofuel cropping practices (i.e. residue removal, plant selection) alter soil microbial community structure, specifically functionality within the C and N cycles. The objectives of the study were to assess 1) overall size and diversity of the microbial community, 2) metabolic activity, and 3) functional genes central to soil N cycling (ammonia monooxygenase, amoA; nitrogenase, nifH; and periplasmic nitrate reductase, napA). Field plots at Purdue Water Quality Field station were established to investigate the following potential biofuel production cropping systems; big bluestem-dominated restored tall grass prairie, maize with residue removal (75%), Miscanthus, sorghum (hybrid PU8168X), and switchgrass; all of which were compared to traditional maize production.  Soil samples were collected three times over a one-year period at two depths (0-5cm, 5-10cm). Microbial biomass, estimated by total extractable phospholipid phosphate (PL-PO4), and bacterial community structure (16S rDNA PCR-DGGE) were unaffected by cropping system. However, metabolic activity, evaluated by basal and glucose-induced respiration and their metabolic quotients (qCO2), and the diversity of functional genes involved in N cycling were strongly influenced by management practices. As indicated by significant differences between and within crop treatments across time with respect to crop establishment. These results indicate that, while the overall size and diversity of soil microbial community is stable, populations central to terrestrial cycling of C and N appear altered by management practices.