THE FATE OF THE CARBON IN SOILS, WHETHER IT IS HELD IN THE EARTH OR RELEASED INTO THE ATMOSPHERE AS CARBON DIOXIDE WHERE IT CONTRIBUTES TO CLIMATE CHANGE, IS DETERMINED PRIMARILY BY THE METABOLISMS OF BACTERIA AND FUNGI LIVING IN THOSE SOILS. AS THESE MICROORGANISMS CONSUME ORGANIC MATTER IN SOIL, THEY CONVERT THE CARBON WITHIN INTO OTHER FORMS THAT CAN BE HELD OF LOST FROM THE SOIL. ALTHOUGH WE KNOW THAT MICROORGANISMS PLAY A DETERMINING ROLE IN SOIL CARBON CYCLING, WE STILL HAVE LITTLE KNOWLEDGE OF WHAT MECHANISMS DRIVE ACTIVITIES THAT HOLD OR RELEASE CARBON FROM SOILS OR WHY SOME SOILS CAN HOLD ON TO MORE CARBON THAN OTHERS. THIS IS DUE, IN PART, TO THE HUGE COMPLEXITY AND DIVERSITY OF MICROBIAL COMMUNITIES, WHICH CONTAIN THOUSANDS OF SPECIES EACH CONTRIBUTING TO CARBON METABOLISM IN DIFFERENT WAYS THAT ARE DIFFICULT OR IMPOSSIBLE TO DIRECTLY OBSERVE. TO TACKLE THIS ISSUE, THIS RESEARCH WILL MEASURE A KEY AND UNIVERSAL TRAIT AMONG SOIL BACTERIA, GROWTH RATES AND PAIR THIS INFORMATION WITH MEASUREMENTS AND PREDICTIONS ABOUT THEIR METABOLIC EFFICIENCY TO ORGANIZE THESE THOUSANDS OF SPECIES INTO SEVERAL BROAD GROUPS WITH PREDICTABLE IMPACTS ON CARBON CYCLING IN SOILS. BACTERIAL GROWTH RATE HAS A WELL-KNOWN TRADE-OFF WITH METABOLIC EFFICIENCY; IN OTHER WORDS, A FASTER GROWING SPECIES RELEASES MORE CARBON DIOXIDE WHEN CONSUMING THE SAME AMOUNT OF CARBON SUBSTRATE COMPARED TO A SLOWER GROWING SPECIES. WE WILL USE THIS FUNDAMENTAL PROPERTY TO UNDERSTAND HOW DIFFERENCES IN COMMUNITY GROWTH RATES IN SOILS CONTRIBUTE TO DIFFERENCES IN THE CARBON FLOWS WITHIN THOSE SOILS.THE EXPERIMENT WILL COMPARE TWO SOILS WITH CONTRASTING LAND MANAGEMENT, ONE SOIL THAT HAS DEPLETED ORGANIC CARBON AND ANOTHER WITH HIGH ORGANIC CARBON. WE WILL INCUBATE SOILS WITH PLANT MATERIAL FOR 30 DAYS AND TAKE SEVERAL MEASUREMENTS THROUGHOUT. FIRST, DNA SAMPLES WILL BE TAKEN REGULARLY AND SEQUENCED WITH AN INTERNAL STANDARD TO ASSESS BACTERIAL COMMUNITY STRUCTURE THROUGHOUT THE INCUBATION. SECOND, RESPIRATION MEASUREMENTS WILL BE TAKEN TO ASSESS THE AMOUNT OF CARBON LOST AS GAS FROM THE SOILS DURING THE INCUBATION. WE WILL ALSO EXTRACT ANOTHER COMPONENT OF MICROBIAL BIOMASS, THE FATTY ACIDS THAT COMPOSE THEIR CELL MEMBRANES TO ASSESS THE AMOUNT OF BIOMASS THAT THE MICROORGANISMS CREATED FROM THE PLANT MATERIAL ADDED AND CALCULATE CARBON USE EFFICIENCY OF THE MICROBIAL COMMUNITIES. WE WILL CALCULATE GROWTH RATES FOR BACTERIA FROM THESE SOILS AND USE COMPARATIVE GENOMICS TO ORGANIZE TAXA INTO BROAD CATEGORIES BASED ON THEIR PREDICTED PHYSIOLOGY. THESE GROUPS CAN THEN BE INTERPRETED IN TERMS OF THE CARBON USE EFFICIENCY MEASURED FROM THE SOILS THEY CAME FROM.THE ULTIMATE GOAL OF THIS PROJECT IS TO SIMPLIFY SOIL BACTERIAL DIVERSITY INTO GROUPS OF ORGANISMS WITH SIMILAR GROWTH STRATEGIES AND IMPACTS ON CARBON CYCLING. A CLEARER UNDERSTANDING OF HOW SOIL MICROBIAL DIVERSITY IMPACTS CARBON CYCLING IN SOILS CAN HELP US MANAGE SOILS FOR GREATER ECOSYSTEM SERVICES, AGRICULTURAL SUSTAINABILITY, AND DECREASED CONTRIBUTION TO CLIMATE CHANGE. THIS KNOWLEDGE WILL ALSO BE INVALUABLE FOR INCORPORATING MICROBIAL PHYSIOLOGY PARAMETERS INTO CLIMATE MODELS AND PREDICTING THE COURSE OF CLIMATE CHANGE.