** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** INCREASING CARBON STORAGE IN SOIL CAN HELP COMBAT CLIMATE CHANGE BY OFFSETTING EMISSIONS FROM FOSSIL FUEL COMBUSTION. THE COLOMBIAN ORINOQU&IACUTE;A IS A VAST SAVANNAH ECOSYSTEM WITH HUGE POTENTIAL TO STORE CARBON VIA IMPLEMENTATION OF DEEP-ROOTED GRASS CULTIVARS. THESE GRASSES PRODUCE LARGE ROOT BIOMASS AND CAN PUMP CARBON DEEP INTO THE SOIL. HOWEVER, THEY REQUIRE ADEQUATE PROVISION OFNUTRIENTS TO AVOID SOIL DEGRADATION AND LOSS OF PREVIOUSLY STORED CARBON. BECAUSE OVER-APPLICATION OF MINERAL FERTILIZERS CAN HARM THE ENVIRONMENT AND LEAD TO GREENHOUSE GAS EMISSIONS, SUSTAINABLE STRATEGIES ARE NEEDED THAT PROMOTE NUTRIENT UPTAKE BY GRASSES IN ORINOQU&IACUTE;A PASTURE SYSTEMS. A PROMISING STRATEGY FOR SUSTAINABLE NUTRIENT MANAGEMENT IS TO PROMOTE SYMBIOTIC RELATIONSHIPS BETWEEN DEEP-ROOTED GRASSES AND ARBUSCULAR MYCORRHIZAL FUNGI (AMF). AMF FEED ON CARBON RELEASED BY PLANT ROOTS AND, IN RETURN, PROVIDE PLANTS WITH NUTRIENTS OBTAINED FROM THE SOIL. WITH AMF, THERE IS THE ADDED BENEFIT THAT THEY HAVE BEEN SHOWN TO CONTRIBUTE TO SOIL CARBON STORAGE VIA TRANSFORMATION OF SOIL ORGANIC MATTER INTO STABLE FORMS. YET, IT IS ALSO KNOWN THAT AMF CAN TRIGGER SOIL PROCESSES THAT LEAD TO CARBON MINERALIZATION AS THEY MINE SOIL FOR NUTRIENTS. TO DETERMINE THE TRUE POTENTIAL OF AMF AS A SUSTAINABLE STRATEGY TO IMPROVE NUTRIENT UPTAKE BY DEEP-ROOTED GRASSES AND INCREASE CARBON STORAGE IN ORINOQU&IACUTE;A PASTURES, IT IS ESSENTIAL TO CHARACTERIZE THE MECHANISMS THROUGH WHICH AMF MAY INDUCE LOSSES OF SOIL CARBON.IN THIS PROJECT, THE DEEP-ROOTED GRASS CULTIVAR UROCHLOA HUMIDICOLA WILL BE GROWN IN POTS OF ORINOQU&IACUTE;A SOIL. IN FIVE OF THE POTS, PLANTS WILL FIRST UNDERGO ROOT INOCULATION WITH AMF. IN THE OTHER FIVE POTS, PLANTS WILL RECEIVE NO INOCULATION. FOR EACH POT, TOTAL PLANT NUTRIENT UPTAKE AND EMISSION OF CO2 WILL BE DETERMINED. DURING THIS EXPERIMENT, A WIDE ARRAY OF SOIL CHEMICAL PARAMETERS (E.G., PH, DISSOLVED NUTRIENTS, PLANT- AND FUNGAL-DERIVED ORGANIC COMPOUNDS) WILL BE MEASURED. THESE MEASUREMENTS WILL BE PERFORMED AT THE MICROSCALE, TO TARGET THE SMALL COMPARTMENT OF SOIL SURROUNDING PLANT ROOTS WHERE MINERALIZATION OF STABLE CARBON IS KNOWN TO PRIMARILY TAKE PLACE. BY COMPARING RESULTS BETWEEN TREATMENTS WITHOUT VS. WITH AMF INOCULATION, WE WILL ELUCIDATE THE EXACT SOIL PROCESSES THROUGH WHICH AMF MAY LEAD TO LOSS OF HIGHLY STABLE SOIL CARBON. AS A FURTHER STEP, WE WILL USE PROCESS-BASED MODELING TO EVALUATE THE EXTENT THAT THESE MICROSCALE PROCESSES CONTRIBUTE TO OUR MEASURED EMISSIONS OF CO2. OVERALL, THIS PROJECT WILL PROVIDE ESSENTIAL MECHANISTIC UNDERSTANDING OF HOW AMF AFFECT THE MICROSCALE SOIL PROCESSES THAT CONTROL CARBON STORAGE. THIS FUNDAMENTAL KNOWLEDGE IS NECESSARY TO EVALUATE WHETHER INCREASED NUTRIENT UPTAKE IN DEEP-ROOTED GRASSES WITH AMF MAY OCCUR AT THE EXPENSE OF SOIL CARBON STORAGE IN TROPICAL PASTURES. MOVING FORWARD, THE RESULTS OF THIS PROJECT WILL SERVE AS A BASIS FOR AGRONOMISTS, FARMERS, AND POLICY MAKERS TO APPROACH THE,URGENT QUESTION OF GRASSLANDS MANAGEMENT FOR CLIMATE MITIGATION IN THE VAST ORINOQU&IACUTE;A.