Smith 9727796 Quantitative evaluation of the global carbon budget, including identification of sources and sinks, will be crucial to our understanding of future climatic and anthropogenic impacts on the global biosphere. To date, models of the global carbon budget have been unable to balance the amount of CO2 released by fossil fuels and modification in land-use with the amount of CO2 remaining in the atmosphere. Of particular concern is the lack of information regarding the spatial and temporal dynamics of the carbon exchange properties of the terrestrial versus oceanic portions of the biosphere, although it has been suggested that the terrestrial biosphere has acted as a net sink for the uptake of CO2 because of imbalances in photosynthesis and respiration due to annual variations in climate. The principle objective of the research will be to identify the annual source/sink dynamics in globally-important ecosystems that are represented in the Rocky Mountains and northern Plains. Identification and quantification of potential terrestrial sinks for CO2 is necessary for predicting future changes that may occur in the global environment. The estimation of net CO2 exchange from vegetative surfaces using remote sensing techniques provides a fundamental data-set for computing the global carbon budget and the existence of carbon sinks that may ameliorate the impact of continued, anthropogenic release of carbon compounds into the atmosphere. However, this approach may also become valuable as a method for establishing physiological status (e.g. photosynthesis) and, thus, the health and vigor of both native and agricultural ecosystems on a global scale. The PI proposes a research plan that characterizes principal ecosystem types of the northern Rocky Mountains and Great Plains. These selected ecosystem types (conifer forest, shrublands, mixed grass prairie and several agricultural types) are excellent representatives of large parts of Earth representing 16%, 18%,11% a nd 16%, respectively, or a total of 61% of the total usable land area of the globe. For some time now, carbon budgets of different ecosystems have been evaluated using measurements of the exchange of CO2 within or above the representative vegetation. These studies require expensive and labor intensive measurements that are affordable when only a small number of geographical locations are monitored. Thus, a substantial sampling problem is inherent in the current leafand canopy-level process submodels, which precludes an accurate coupling with atmospheric circulation models and ultimate extrapolation to broader geographic scales. In the current proposal, aircraft measurements of eddy transport of water vapor and C02 exchange will be combined with isotopic data to estimate CO2 fluxes on an annual and seasonal basis. Results will be scaled directly up to the northern Rocky Mountains and northern Great Plains with regional, digital coverage's together with GIS methods and ecosystem modeling techniques in order to produce a regional estimate of carbon fluxes for a significant portion of North America. Incident sunlight, precipitation, soil and plant moisture, air temperature and humidity will be monitored concurrently with CO2 flux measurements. In addition, the capability for measuring natural isotopes of carbon and water provides an accurate and reliable method for estimating the component sources of CO2 that comprise measured values of net CO2 flux . Net fluxes will be partitioned into a balance of particular sources (i.e. atmosphere, plant photosynthesis and respiration, soil respiration, etc.), according to differences in discrimination between stable isotopes contained in each environmental component (e.g. leaf and soil organics; leaf, stem, and soil water, etc.). Overall, these results will will provide the groundwork for testing process models that extrapolate globally. Both "topdown" and "bottom-up" approacheswill be compared by using measurements taken sim ultaneously at the plant level, above the canopy (eddy correlation tower), and with aircraft sampling. Although we will be focusing on the more difficult problems of spatial heterogeneity within this region, the applicability of our results from this region should be important for extrapolating to similar ecosystems across the globe (e.g. Asian continent).
