Effects of Elevated Atmospheric Carbon Dioxide on Soil Carbon in Terrestrial Ecosystems of the Southeastern United States

As one travels through the rural southeastern landscape, even the most casual observer will note three dominant vegetation types. One cannot help but notice the predominance of forests—both natural and planted—as the Southeast is the nation’s “wood basket,” producing more wood fiber than any other area of the country. The casual traveler will also see a variety of agricultural row crops being grown. These change from cotton, corn, soybeans, and peanuts to tobacco and vegetables as one visits the varying geographic regions of this diverse area. The final land use one will observe is pasture lands; these may be supporting herds of beef cattle or may be managed to produce hay for winter feeding. All of these types of vegetation have the ability to take carbon from the atmosphere and store it either as standing biomass (including plant roots) or in soil. However, the Earth’s atmosphere is changing, and increasing carbon dioxide (CO2) concentration is one of the most studied and best documented of these changes. How will this rising CO2 affect the vegetation types of the Southeast and how will these plants impact the continuing rise in the concentration of atmospheric CO2? Finally, can these varying land uses help mitigate the increase in atmospheric CO2 by storing C in soil, and can we, as researchers, find ways to manage these systems to increase the amount of CO2 taken from the atmosphere and stored in the soil? These are the questions that will be investigated and explained in the following chapter. When considering soil C storage, there are several parameters and processes (as well as impacts on these) that must be taken into account. The first parameter to consider is inputs. Carbon can enter soil via plant processes such as root exudation, sloughing of root cells, and other processes associated with root growth. These inputs, however, are readily decomposable and probably do not add to soil C pools residing more than a few days to weeks. The majority of soil C comes directly from vegetation itself, as aboveground residue or litter and as plant roots. Therefore, it is important to consider plant growth and biomass production processes when attempting to understand soil C sequestration. Not only is