The research proposed here will assess the importance of feedbacks between plant productivity, biomass removal due to fire and herbivory, and element cycling in grassland ecosystems. Conceptual models of interactions among these processes will be evaluated in mixed grasslands of the southern Great Plains. These models are distinguished by the relative importance they assign to feedbacks between plant tissue quality and soil nitrogen mineralization rates. Models emphasizing feedbacks differ in the nature (positive or negative) of specific feedback mechanisms. Models assume minimal importance to feedbacks identify different factors (climate vs. decoupling of C and N cycles) as primary regulators of fertility and plant productivity. Existing data collected by these researchers suggest that that modulation of plant inputs to soils by fire and herbivory limit microbial C pools in these grasslands, thereby minimizing feedbacks to C and N cycling. The investigators request support for analysis of existing plant and soil samples to assess the degree of decoupling between C and N cycling in soil pools.
