ATM-9312153 Fall Although tremendous quantities of volatile organic compounds (VOCs) are released from vegetation into the atmosphere annually, it is not clear why plants expend a considerable amount of energy synthesizing volatile and reactive VOCs. The fact that these emissions shape global tropspheric chemistry underscores the importance of developing an understanding of the underlying processes that regulate emissions. Plants evolved under conditions which, due to man's influence, are much different that present day conditions throughout the industrial world. Until we better understand the basic mechanisms that are responsible for the emission of these compounds, we will not be able to assess the effects that these changing conditions have on vegetation currently, or how these plants and their emissions will respond to further global change. This research will address three fundamental questions: 1) What are the underlying mechanisms for the biosynthesis and emission of major classes of VOCs to the atmosphere? 2) What are the major physical and biological "drivers" that regulate VOC emissions? 3) How do VOCs exit plant surfaces? The biogenic VOCs to be studied include those organics that make up the majority of natural emissions: the non-methane hydrocarbons, isoprene and monoterpenes; and the oxygenated hydrocarbons, methanol, ethanol, acetaldehyde, acetone, 2 methyl-3-buten-2-ol (methyl butenol), and the hexenal family (hexenal, hexenyl acetate). For example, detailed experiment will examine; 2) the mechanisms of methanol, acetone methyl butenol, and isoprene biosynthesis; b) the possibility that isoprene is a "leaky" metabolic intermediate and that leafiness may explain why isoprene-emitting plants range form high to low emitters: and c) the role of light, temperature, humidity, carbon dioxide concentration, stomatal conductance and leaf development as major "drivers" of VOC emissions. In addition, d) experiments will be conducted to establish the role of cuticle surfaces and stomatal pores in the exit of VOCs from leaves, including the emission of monoterpenes from conifer needles. These studies should provide new insights into how and why plants emit VOCs, reduce uncertainties about the "drivers" of emissions, and allow prediction of future VOC emissions in response to global change.
