POTENTIAL IMPACTS OF ELEVATED CO2 AND ABOVEGROUND AND BELOWGROUND LITTER QUALITY OF A TALLGRASS PRAIRIE

Increased atmospheric CO2 will likely impact the productivity of arid and semiarid ecosystems through increased C, N, and water use efficien cies at the individual plant level. Tallgrass prairie has had increase d above- and belowground biomass production under elevated CO2, primar ily due to increased water use efficiency. There is an apparent decrea sed N requirement to sustain increased productivity in CO2-enriched ta llgrass prairie, and C:N ratios of plant litter above and below ground have increased. The tallgrass prairie ecosystem level response to ele vated CO2 on the C cycle could potentially increase C storage. Reduced litter quality associated with elevated CO2 in tallgrass prairie has the potential to reduce decomposition rates, and ruminant digestion ra te of plant biomass apparently has been lowered. Reduced intake by rum inants would shunt more of the plant biomass directly into the detrita l food chain, thereby slowing decomposition further. The potential imp act is for increased C to be retained as soil organic matter in the ta llgrass prairie.