||By storing and releasing carbon, ecosystems on land influence the rate of climate change. However, in the models used to project future climates, some of the important processes affecting carbon storage are coarsely represented or omitted. This project will examine an omitted process: how plants can affect carbon storage through releases of easily decomposed materials from their roots, and how future conditions could affect the way these “exudates” interact with the carbon compounds already present in soil. The project will assess how changes in soil moisture and temperature affect inputs of new carbon to the soil from plant communities, and the rate of decomposition of older soil carbon once new carbon has been added. The project will take place at the Boston-Area Climate Experiment. At this site, plots of a meadow-like plant community with tree seedlings are grown under twelve different climatic conditions, with four different amounts of warming and three levels of precipitation. New carbon inputs will be assessed using mesh cylinders of soil that will be placed into the ground at the beginning of the experiment, so that roots and fungi (or fungi only, or neither) can grow in, and removed at the end. Decomposition of carbon inputs will be examined by slowly injecting known carbon-containing solutions (or water) into the soil at known rates and monitoring the carbon dioxide released by the soil microbes. This exploratory project will test the feasibility of these seldom-tried experimental approaches, and produce initial results indicating how climatic changes can affect interactions between new and old carbon. Results from the project will inform the design of more comprehensive experiments that will improve our models of the exchange of carbon between the land and atmosphere in a changing world.