Some Hydrogen and Carbon Isotope Studies on Plants and Their Environments

The ratios D/H and C13/C12 were determined for plants from locations varying in position and elevation. In t his respect plants of the same species were shown to behave similarly. Carbon results suggest that plants closely reflect the composition of atmospheric CO2. Hydrogen results, however, seem affected by local variations in ground-water composition, with large plants and plants removed from contact with ground moisture showing the least effect. A general decrease in hydrogen and carbon isotopic weights was observed in plants from the western slopes of the Sierra Nevada, while plants from the western slopes of the White Mountains were observed to be relatively constant in this respect. The general eastward motion of air masses over the Sierra and into Owens valley before reaching the White Mountains is a possible explanation for this difference. Differences between hydrogen isotopic compositions of ground-waters and their associated plants are suggested as ·possible indicators of climatic condition.