Physiology of Isoprene Emission from Plants

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Isoprene emitted from trees is the largest source of hydrocarbons in the atmosphere. Isoprene decomposition in the atmosphere is rapid and causes lower atmosphere formation, acid rain, and blue hazes. Only some plants produce isoprene, it is a common trait in trees ferns, and tropical plants. The production of isoprene is closely associated with the carbon photosynthesis, but mechanism of isoprene formation and its function in plants is unknown. To better understand isoprene emission and to predict changes in isoprene emission which may occur in the future the effect of growth conditions on isoprene synthesis will be studied. The mechanism of isoprene synthesis will also be studied. Previous results indicated that when oak trees are grown in high carbon dioxide atmospheres the rate of isoprene emission can double. In this project the effect of carbon dioxide will be further tested and the effect of increased temperature, believed to be a consequence of increased carbon dioxide, will also be tested. Rates of acclimation to the various growth conditions will be assesed. The pathway of isoprene synthesis will be investigated using techniques developed to study photosynthesis. Stable isotopes (nonradioactive) of carbon and hydrogen will be used to trace the pathway of carbon during isoprene synthesis in leaves. These studies are important because of the role of biogenic isoprene in atmospheric chemistry, because isoprene synthesis can be a fast, nondestructive measure of important, nonphotosynthetic carbon metabolism inside chloroplasts (e.g. carotenoid synthesis), because isoprene synthesis can affect the overall carbon budget of plants.