As captured in the above concepts an over-arching goal of our carbon cycle activities is to understand the mechanistic controls over the fate, transport, and residence time of carbon in the earth system's reservoirs. These mechanistic studies (laboratory and field-based) are then used to inform and ultimately, improve, models of increasing complexity to assist in predicting the role of the carbon cycle in future climate change. A simple question is whether or not the future carbon cycle will be a net source or sink of CO2 to the atmosphere. Many of the modern process and modeling studies focus on seasonal to interannual variability. However, much of the carbon on the landscape is in separate reservoirs with turnover times that are multi-decadal to millennial. It is the controls on these longer term pools or reservoirs that is a critical unknown in the face of rising greenhouse gases and climate change and uncertainties of the terrestrial biosphere as a future global sink or source of atmospheric CO2.