9524129 Coughenour This research is to develop capabilities for numerically assessing the responses of grassland ecosystems to atmospheric changes associated with increasing levels of greenhouse gases, particularly carbon dioxide (CO2). Currently, there are at least three major deficiencies in our abilities to perform these assessments. The first is a lack of computer models which have been calibrated and tested against field CO2 exposure experiments in grasslands. Accordingly, a focus of this research will be to collaborate with scientists working on an ongoing field exposure study in Kansas. An existing model of grassland ecosystem function and plant responses to CO2 and weather will be used for this purpose. Secondly, models that faithfully represent current understanding of plant physiology must be coupled with models that represent soil processes such as decomposition, nutrient cycling and water storage and flows to understand how whole ecosystems respond to atmospheric change. For example, it is possible that nutrient cycling rates will constrain otherwise positive plant growth responses to elevated CO2. Linked state-of-the-art plant physiological and soil process models will be employed in the proposed research. Thirdly, terrestrial ecosystem processes of water, carbon and energy exchange with the atmosphere have potentially significant effects on ecosystem responses to atmospheric change but have been poorly examined in past modeling research. This research will link ecological and atmospheric models to assess the role of atmospheric processes, particularly large-scale fluxes of water vapor and energy. These results will feedback onto plant growth through altered plant water use efficiency, and resultant responses of nutrient cycling rates. Grasslands, climate, and the interactions between climate and grasslands will be explored through linking these various models.
