**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** LOBLOLLY PINE (PINUS TAEDA L.) IS ONE OF THE MOST INTENSIVELY MANAGED AND ECONOMICALLY IMPORTANT FOREST SPECIES IN THE WORLD. IN THE SOUTHEASTERN US, PHOSPHORUS (P) INPUTS AT PLANTATION ESTABLISHMENT ARE OFTEN REQUIRED TO OPTIMIZE PRODUCTION, BUT OUR UNDERSTANDING OF COMPLEX INTERACTIONS AMONG SOIL CHEMICAL PROPERTIES, THE SOIL BIOLOGICAL PROCESSES THAT CONTROL NUTRIENT AVAILABILITY, AND THE INFLUENCE OF PREVIOUS FERTILIZATION RATES REMAINS LIMITED. WE KNOW PINE-ASSOCIATED ECTOMYCORRHIZAL FUNGI EXPLORE SOIL VOLUME AND ENHANCE NUTRIENT AVAILABILITY TO TREES BUT ARE UNCERTAIN HOW FERTILIZATION PRACTICES AFFECT THE SOIL-PLANT-MICROBIAL SYSTEM TO ALTER NUTRIENT AVAILABILITY BOTH IN THE SHORT AND LONG TERM. WE HAVE THE UNIQUE OPPORTUNITY TO UTILIZE LONG-TERM, REPLICATED FIELD TRIALS IN LOBLOLLY PINE PLANTATIONS THAT RECEIVED INCREASING RATES OF P APPLICATION IN THE PREVIOUS ROTATION AND ARE CURRENTLY BEING HARVESTED AND REPLANTED. WE WILL EXPERIMENTALLY MANIPULATE ESTABLISHMENT P FERTILIZATION IN THESE GEOGRAPHICALLY-DISTRIBUTED SITES WITH A WIDE RANGE OF SOIL CHARACTERISTICS TO INVESTIGATE MECHANISTIC UNDERPINNINGS DETERMINING SOIL NUTRIENT SUPPLY. THROUGH A COMBINATION OF TECHNIQUES SUCH AS MICRODIALYSIS, ION-EXCHANGE MEMBRANES, SELECTIVE DISSOLUTION ANALYSIS, FRACTIONATION OF P SUB-POOLS, AND CHARACTERIZATION OF THE FUNGAL MICROBIOME AND MYCORRHIZAL BIOMASS, WE WILL EVALUATE THE ABIOTIC AND BIOTIC DRIVERS OF P AVAILABILITY, WITH LOBLOLLY PINE GROWTH RESPONSE AS THE FINAL BIO-INDICATOR. OUR GOAL IS TO ENHANCE THE CAPACITY TO PREDICT NUTRIENT LIMITATIONS AND CROP TREE GROWTH RESPONSE TO FERTILIZATION. THIS WORK IS DIRECTLY RELEVANTTO ENHANCE PRODUCTIVITY, SOIL HEALTH, AND ENVIRONMENTAL STEWARDSHIP.