BIOINOCULANT PRODUCTS IN AGRICULTURE REPRESENT ONE OF THE FASTEST-GROWING MARKETS IN THE WORLD, WITH AN APPROXIMATE 17% ANNUAL INCREASE AND AN ANTICIPATED MARKET VALUE OF $12 BILLION US BY 2026. NEW REGULATORY CONSTRAINTS PLACED ON THE AGROCHEMICAL INDUSTRY ARE EXPECTED TO REDUCE CONSUMER DEMAND FOR CHEMICAL INPUTS AND POSITION THE MICROBIAL-BASED INOCULANTS INDUSTRY TO ABSORB PART OF THIS CURRENT $250 BILLION MARKET. THE ADOPTION OF BIOLOGICAL TOOLS OFFERS A PROMISING PATHWAY TOWARD MORE RESILIENT, EFFICIENT, AND ECOLOGICALLY RESPONSIBLE AGRICULTURAL SYSTEMS, ULTIMATELY SHAPING THE FUTURE OF SUSTAINABLE FOOD PRODUCTION. HOWEVER, THE VARIABLE EFFICACY OF MICROBIAL INOCULANTS AND OUR LIMITED UNDERSTANDING OF THEIR EFFECTS ON SOIL HEALTH AND THE MICROBIOME HAVE SEVERELY HAMPERED THE WIDESPREAD ADOPTION OF MICROBIAL-BASED PRODUCTS. THIS PROPOSED RESEARCH WILL DIRECTLY CONTRIBUTE TO IMPROVING MICROBIAL INOCULANT SUCCESS AND ADVANCE OUR UNDERSTANDING OF THE INTERANNUAL EFFECTS OF BIOLOGICAL AMENDMENTS IN SOIL. AIMS 1 AND 2 WILL LEVERAGE ECOLOGICAL THEORY TO EXPERIMENTALLY MANIPULATE THE COMPONENTS OF PROPAGULE PRESSURE (E.G., NUMBER OF INOCULATIONS AND NUMBER OF CELLS PER INOCULATION) TO ENHANCE INOCULANT ESTABLISHMENT, IMPROVE PLANT PERFORMANCE, AND UNDERSTAND THE IMPLICATIONS OF MICROBIAL INOCULATIONS ON SOIL HEALTH. THIS STUDY FOCUSES ON TWO DISTINCT ORGANISMAL TYPES (I.E., ARBUSCULAR MYCORRHIZAL FUNGI - RHIZOPHAGUS IRREGULARIS, AND BACTERIA - BACILLUS LICHENIFORMIS) ASSOCIATED WITH MICROBIAL-MEDIATED PHOSPHORUS ACQUISITION IN PLANTS.OUR EXPERIMENTAL APPROACH WILL ASSESS THE EFFECTS OF MICROBIAL AMENDMENTS ON PLANT PERFORMANCE, THE SOIL MICROBIOME, AND A SUITE OF SOIL HEALTH PARAMETERS. WE WILL GROW PLANTS IN A CLIMATE-CONTROLLED GREENHOUSE OVER TWO CONSECUTIVE YEARS. AT THE END OF EACH GROWING SEASON, WE WILL USE HIGH-THROUGHPUT GENOMIC TOOLS (E.G., 16S AND ITS AMPLICON SEQUENCING) TO DESCRIBE THE SOIL MICROBIOME FOLLOWING THE APPLICATION OF BIOLOGICAL AMENDMENTS AT DIFFERENT RATES. ADDITIONALLY, WE WILL EMPLOY A SUITE OF BIOGEOCHEMICAL MEASUREMENTS TO UNDERSTAND THE IMPLICATIONS OF MICROBIAL AMENDMENTS ON SOIL HEALTH AND THE ASSOCIATED TEMPORAL PATTERNS OVER TWO GROWING SEASONS. IN PARTICULAR, THE DATA GENERATED FROM THIS EXPERIMENT WILL DIRECTLY CONTRIBUTE TO IMPROVING MICROBIAL INOCULATION METHODS AND INCREASING MICROBIOME-MEDIATED PHOSPHORUS ACQUISITION IN PLANTS. TOGETHER, THIS WORK WILL LEAD TO A DECREASED DEPENDENCE ON SYNTHETIC AGROCHEMICALS AND PROMOTE SUSTAINABLE AGRICULTURAL PRACTICES.