** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** 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 ONTWO DISTINCT ORGANISMAL TYPES (I.E., ARBUSCULAR MYCORRHIZAL FUNGI - RHIZOPHAGUS IRREGULARIS, AND BACTERIA - BACILLUS LICHENIFORMI) 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 CONSECUTIVEYEARS. AT THE END OF EACH GROWING SEASON, WE WILL USE HIGH-THROUGHPUT GENOMIC TOOLS (E.G., 16S AND ITS AMPLICON SEQUENCING) TODESCRIBE THE SOIL MICROBIOME FOLLOWING BIOLOGICAL AMENDMENTS APPLIED AT DIFFERENT RATES. ADDITIONALLY, WE WILL EMPLOY A SUITE OF BIOGEOCHEMICAL MEASUREMENTSAND SOILASSAYS TO UNDERSTAND THE IMPLICATIONS OF MICROBIALAMENDMENTS ON SOIL HEALTH AND THE ASSOCIATEDTEMPORAL PATTERNS OVER TWO GROWING SEASONS. IN PARTICULAR, THE DATA GENERATED FROM THIS EXPERIMENT WILL DIRECTLY CONTRIBUTE TOIMPROVING MICROBIAL INOCULATION METHODSAND AID IN UNDERSTANDING MICROBIAL AMENDMENTS' IMPLICATIONS FOR INCREASING PHOSPHOROUS ACQUISITION. TOGETHER, THIS WORK WILLLEADTO A DECREASED DEPENDENCE ON SYNTHETIC AGROCHEMICALS IN PRODUCTION AGRICULTURE SYSTEMS AND PROMOTE SUSTAINABLEPRACTICES IN PRODUCTION AGRICULTURE.