Environmental Effects on Stable Isotopes and Carbon Cycle Processes in Agricultural Settings of Iowa.

German Mora, Department of Geological and Atmospheric Sciences, Iowa State University, Ames, Iowa

The fate of anthropogenic emissions of carbon dioxide is inferred from the variability of atmospheric CO₂ concentrations and their oxygen- and carbon- isotopic abundances.  For simplicity, it is assumed that terrestrial ecosystems exhibit distinct and constant isotopic abundances.  However, leaf-level studies indicate variable isotopic content that depends on prevailing environmental conditions.  The goal of our proposed project is to evaluate the diurnal and seasonal variability of isotopic abundances of CO₂ in corn and soybean fields of Iowa, and to assess the relationship between their isotopic variability and changes in temperature, rainfall, and soil moisture.  We hypothesize that isotopic abundances fluctuate seasonally following changes in temperature and rainfall.  Results from this proposed project would test the variability of current modeling efforts that assume constant isotopic abundances.

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