A study of the relationship of climate and vegetation to the stable isotope chemistry of grassland soils in the Great Plains will be conducted. Six study sites in differing temperature, moisture, and vegetation regimes have been selected and will be monitored for biomass production, dust accumulation, and soil CO2 production. This background information, in conjunction with climatic data, will provide a basis for interpreting the delta 13C and delta 180 of pedogenic carbonate in these soils. An investigation of the data 13C and chemical composition of occluded C in opal phytoliths is the major goal of this research. The delta 13C of opal phyoliths extracted from the soil will be examined and it will be determined whether it represents the ratio of C3 to C4 vegetation and the delta 13C of the soil organic matter. The work will demonstrate the suitability of opal phytoliths, as well as pedogenic carbonate, as tools in paleoenvironmental reconstruction studies. This research should be of fundamental ecological importance as well as potentially useful in providing a significant new method for soil science in general. The Ecosystem Studies Program recommends support.