SUSTAINABLE AGRICULTURAL PRACTICES ARE INCREASINGLY IMPORTANT DUE TO RISING INPUT COSTS AND GREATER CONCERN ABOUT ENVIRONMENTAL IMPACTS. BIOLOGICAL SOIL CRUSTS (BSCS), A NATURALLY-OCCURRING PHOTOTROPHIC CONSORTIUM OF MICROORGANISMS ON THE SOIL SURFACE, WERE RECENTLY IDENTIFIED IN LOCAL PRODUCER FIELDS. BSCS ARE WELL-DOCUMENTED IN ARID ECOSYSTEMS WHERE THEY ARE A SOURCE OF FIXED NITROGEN (N) AND HELP IMPROVE SOIL MOISTURE. THIS PROPOSAL IS, TO OUR KNOWLEDGE, THE FIRST TO CHARACTERIZE BSCS IN AGROECOSYSTEMS WHERE THEY COULD BENEFIT CROP PRODUCTION BY INCREASING SOIL N AVAILABILITY AND ENHANCING WATER RETENTION.BSCS FROM CONTRASTING ECOSYSTEMS OF TREE-CROPS IN FLORIDA TO DRYLAND WHEAT FIELDS AND VINEYARDS IN OREGON WILL BE CHARACTERIZED FOR CHANGES IN MICROBIAL COMMUNITY STRUCTURE, COMPOSITION, AND ABUNDANCE BY HIGH THROUGHPUT AMPLICON SEQUENCING AND QUANTITATIVE PCR OF THE FUNGAL, ARCHAEAL, AND BACTERIAL POPULATIONS. ALONG WITH FUNCTIONAL DIVERSITY, THE CAPACITY FOR N CYCLING WILL BE ASSESSED BY QUANTIFYING RATES OF N2-FIXATION, NITRIFICATION, AND DENITRIFICATION. LABORATORY MANIPULATION OF LIGHT INTENSITY, MOISTURE REGIME, AND FERTILIZATION WILL REVEAL ENVIRONMENTAL FACTORS DRIVING BSC DEVELOPMENT AND FUNCTION. THE BENEFIT OF BSCS TO PLANT GROWTH WILL BE TESTED IN GREENHOUSE STUDIES WITH MODEL CROPS AND USING 15N TECHNIQUES TO TRACE THE UPTAKE AND FATE OF BSC N.OUR PROJECT DIRECTLY ADDRESSES THE INTEREST IN UNDERSTANDING KEY BIOGEOCHEMICAL PROCESSES AND MANAGEMENT PRACTICES FOR "SOIL HEALTH AND MICROBIAL COMMUNITIES." THE PROPOSED RESEARCH WILL ALSO ADVANCE OUR UNDERSTANDING OF THE ECOLOGY OF AGRICULTURAL BSCS AND IDENTIFY WHETHER THESE MICROBIAL CONSORTIA CAN IMPROVE SUSTAINABILITY OF AGROECOSYSTEMS THROUGH REDUCTION OF NUTRIENT AND WATER INPUTS.