SOILS REPRESENT THE LARGEST STOCK OF CARBON ON LAND. THE AMOUNT OF ORGANIC CARBON STORED IN SOILS IS A BALANCE BETWEEN THE INPUTS OF ORGANIC CARBON BY PLANTS AND MICROORGANISMS AND THE RESPIRATION OF SOIL ORGANISMS AS THEY DECOMPOSE SOIL ORGANIC CARBON. UNDERSTANDING THIS BALANCE IS IMPORTANT BECAUSE ORGANIC CARBON CONTROLS SOIL FERTILITY AND RESILIENCE AGAINST EROSION, AND RESPIRATION REPRESENTS THE LARGEST TERRESTRIAL SOURCE OF CO2 TO THE ATMOSPHERE. FURTHERMORE, SOME RESPIRATION IN SOILS IS ALSO A SOURCE OF POTENT GREENHOUSE GASES, SUCH AS N2O AND CH4. ESPECIALLY AT A TIME WHEN CARBON DRAWDOWN IS ESSENTIAL FOR GLOBAL HUMAN HEALTH, IDENTIFYING THE MECHANISMS THAT CONTROL GASEOUS EMISSIONS FROM SOILS IS IMPERATIVE. WHILE MUCH WORK HAS BEEN DEVOTED TO UNDERSTANDING THE PROCESSES THAT GOVERN SOIL CARBON STORAGE AND RESPIRATION, OUR CURRENT SCIENTIFIC UNDERSTANDING STILL DOES NOT CAPTURE THE VARIABILITY IN SOIL CARBON STOCKS AND FLUXES OBSERVED IN THE FIELD. ACCURATE UNDERSTANDING OF THE CONTROLS OF CARBON IN SOIL IS CRUCIAL FOR ACCURATELY PREDICTING SOIL NUTRIENT CONTENT. IN ADDITION, SUCH UNDERSTANDING WILL INCREASE PRECISION OF THE SOIL CARBON CYCLE IN EARTH SYSTEM MODELS FROM THE WATERSHED TO GLOBAL SCALE. THEREFORE, WITH THIS WORK I WILL EXAMINE RESPIRATION IN THE FUNDAMENTAL UNIT OF SOIL PROFILES, AGGREGATES, AS A KEY SOURCE OF THE UNACCOUNTED VARIABILITY IN SOIL CARBON STOCKS AND FLUXES.WITH THE INITIAL AWARD FOR THIS PROJECT, I DID MUCH TOWARDS IDENTIFYING THE LAND-USE AND SOIL PROPERTIES INHERITED FROM PARENT ROCK THAT CONTROL THE BIOGEOCHEMICAL IMPACT OF AGGREGATES ON THE SOIL CARBON CYCLE. HOWEVER, WITH THE TRANSFERRED AWARD, I WILL FOCUS ON THE ROLE THAT PLANT ROOTS PLAY IN CONTROLLING MICROBIAL RESPIRATION IN SOIL AGGREGATES. TO ACHIEVE THIS GOAL, THE GRADUATE STUDENT RECRUITED TO WORK ON THIS PROJECT WILL GROW GRASS SPECIES COMMON IN OKLAHOMA AND USE NOVEL SOIL GAS CHARACTERIZATION METHODS TO IDENTIFY THE MICROBIAL RESPIRATION PROCESSES WITHIN SOIL AGGREGATES. THIS WORK WILL BE CONDUCTED IN THE LABORATORY TO ALLOW FOR CONTROLLED CONDITIONS AND MORE FREQUENT MEASUREMENT OF SOIL GAS CONCENTRATIONS. THIS LABORATORY INVESTIGATION WILL BE COMPLEMENTED BY A FIELD-BASED PROJECT, IN WHICH A STUDENT WILL BE USING MINI-RHIZOTRONS AND SOIL GAS WELLS TO MAKE SIMILAR MEASUREMENTS OF ROOT RESPIRATION IN SITU. THIS PROJECT WILL SERVE AS VALUABLE TRAINING IN RESEARCH AND SOIL SCIENCE FOR THE GRADUATE STUDENT.THIS NEW WORK ON ROOTS AND SOIL RESPIRATION THAT WILL COMPLEMENT THE EXPERIMENTS I CONDUCTED DURING MY DOCTORAL STUDIES WILL BE BROADLY RELEVANT TO SOIL SCIENTISTS ACROSS THE UNITED STATES. THIS NEW KNOWLEDGE ON THE CONTROLS OF ROOTS ON THE CARBON CYCLE IN SOIL AGGREGATES GAINED FROM THESE EXPERIMENTS WILL SERVE AS THE BASIS FOR CHANGING CURRENT CARBON CYCLE MODELS IN ORDER TO INCREASE THE EXPLAINED VARIANCE IN SOIL CARBON FLUXES. ADDITIONALLY, THESE MODIFICATIONS WILL ALSO RESULT IN GREATER CONFIDENCE IN SOIL NUTRIENT MODELS USED BY PRODUCERS.IN A TIME OF CHANGING CLIMATE AND LAND-USE, THIS WORK WILL SERVE AS A CRITICALLY IMPORTANT SOURCE OF INFORMATION ON THE FUNCTIONING OF SOILS.