This project will generate a change in knowledge about the role plant diversity and community composition play in stable soil carbon formation. We will be able provide stakeholders with more clear guidance regarding when diverse grasslands can contribute to the SOC stabilization. This is of particular interest to producers managing lands in Conservation Reserve Programs (CRPs). Our work will provide information on how to maximize conservation reserve programs (CRP) to mitigate climate effects. Our work will also be of interest for stakeholders managing biofuel crops. Switchgrass, a common grass chosen for bioenergy feedstocks, is one of the 18 species in a plant diversity and precipitation manipulation experiment,and was specifically selected for experiments in objectives 1 and 2. Often bioenergy feedstocks, like switchgrass, are grown in monoculture, which could limit their aboveground productivity and ability to stabilize soil C. Our work will provide useful guidance on how best to grow bioenergy stocks, such as switchgrass, in monoculture or mixture to maximize their ability to sequester C in stable forms and reduce CO2loss from the system.