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Microbial Ecology of Sustainable Biofuel Production Heather Reynolds, Jim Bever, and Keith Clay IU Department of Biology

Biofuels can reduce dependence on foreign oil and mitigate global climate change, while boosting important sectors of the economy and enhancing national security. The dominant U.S. biofuel crop (corn), however, is grown with heavy inputs of chemical fertilizers and pesticides, which require substantial inputs of fossil fuels. Further, corn and other conventional biofuel crops are grown on agricultural land. Thus, conventional biofuel crops are net sources of greenhouse gases and compete with food crops. Realizing the promise of biofuels depends on minimizing fossil fuel inputs while optimizing productivity on abandoned or marginal lands. Corn Switchgrass (Panicum virgatum) The challenge can be met by utilizing plant-microbe relationships from nature that promote productive biofuel crop yields on marginal or degraded lands (e.g., strip-mined lands). Native prairie plants such as switchgrass (Panicum virgatum) have a number of traits (including perennial growth, high resource use efficiency, and high nutrient recycling potential) suited to optimizing yield in degraded soils. Little is known, however, about the underlying microbial ecology of these systems. Native grasses interact with numerous microorganisms in the soil and in plant leaves and roots. Three key microbial functional groups are nitrogen-fixing bacteria, arbuscular mycorrhizal fungi, and fungal endophytes. Nitrogen-fixing bacteria inhabit plant roots in a tight symbiotic relationship in which plant sugars are exchanged for nitrogen or associate more loosely with above- and below-ground plant parts as free-living bacteria. Arbuscular mycorrhizal fungi form symbiotic associations with plant roots in approximately 80 percent of all land plants, transferring phosphorus to the plant in exchange for sugars. Endophytes inhabit the shoots of many turf, pasture, and wild grasses. They produce alkaloids and hormones that increase pest resistance, plant growth, and drought tolerance. Recent work from the Reynolds, Bever, and Clay labs reveals that interactions between plants and microbes can be very complex. For example, plant responses to microbes can vary with the identity of plant and microbe, soil nutrients, and microbial density. Strip-mined land Rhizosphere bacteria on root Arbuscular Mycorrhizal Fungus (AMF) Endophyte fungus growing inside grass leaf Building on emerging understanding of plant-soil-microbe interactions requires identification, development, and optimization of microbial inoculations for improved biofuel production. Indiana University-Bloomington has a strong group focused on the study of plant interactions with soil and symbiotic microorganisms. Its researchers have identified, isolated, and manipulated microbes in the laboratory and the field, have expertise in the analysis of soil nutrients and bacterial and fungal diversity, and their initial work suggests combinations of inoculants that maximize grassland productivity. The immediate goals of their research are to isolate nitrogen-fixing bacteria, phosphorus-mobilizing arbuscular mycorrhizal fungi, and endophytic fungi from native switchgrass and grassland communities. They also seek to utilize factorial inoculations of these microbial groups in field soils and in greenhouse trials. This research will advance basic scientific knowledge of microbial biodiversity and plant-soil-microbe interactions and their effects on plant growth. The research also has applied value in developing sustainable biofuel production of switchgrass and other native grassland species.