The isotopic composition of plant leaves provides information about the amount of water lost per unit of plant growth. Further, recent data show that carbon and hydrogen isotope measurements can be used to determine whether water vapor in the forest canopy came from the soil, via evaporation, or from plants. In this study, the isotopic composition of leaves and canopy water vapor will be investigated to understand and predict the responses of vegetation to potential changes in precipitation, and to identify possible vegetation feedbacks to ecosystem-scale water cycling. The project is designed to test three hypotheses relating vegetation-atmosphere water cycling at the James San Jacinto Mountain Reserve of the University of California Natural Reserve System, near University of California, Riverside (UCR). The three hypotheses integrate plant physiology to ecosystem-level processes, and will be evaluated in the context of understanding the responses of vegetation to predicted changes in precipitation regime. This project will support directly the development of new stable isotope facilities at UCR, and thus contribute to state-of-the-art scientific infrastructure. It also will promote the professional development of a new assistant professor, and his interaction with a pioneering group of local scientists with similar interests. Furthermore, work at the James Reserve will benefit, and benefit from, intensive on-going studies at that location, which has become a hotbed of innovative and experimental techniques. The novelty of this investigation will allow opportunities to teach this technique to students and further its use.
