As atmospheric CO2 concentrations increase there almost certainly will be alterations in the flux of C from plants to the soil. It is likely that alterations will be accompanied by changes in the allocation of C to organic structures and to soil processes. These changes have the potential for further altering the structure and function of terrestrial ecosystems. While there has been increasing recognition of the importance of soil-mediated responses to global climate change, the nature and magnitude of these responses are not well understood.