Biology, Controls and Models of Tree Volatile Organic Compound Emissions
Discoveries that plants are in part responsible for the blue haze commonly observed in the atmosphere above many forests (Went 1960; Rasmussen andWent 1965) and for the tropospheric ozone pollution in many forested urban and suburban areas (Rasmussen 1972; Chameides et al. 1988) have compelled researchers to ask what are the plants emitting, how much is being emitted and how do these emissions impact our environment? These very important questions are at the heart of a highly interdisciplinary research field: biogenic volatile organic compounds (BVOC) in the biosphere–atmosphere component of the Earth system.
Fritz Went, a plant physiologist famous for discoveries on plant growth regulators, was also intrigued by the potential for plants to form atmospheric hazes above forests. He hypothesized that the organic compounds emitted from plants, many of which he could detect with his own sense of smell, contributed to this haze. In 1960, he made measurements on the mass of leaf oils in shrubs from the Western United States and estimated global terpene emissions to be 175 Tg C year1 (1 TgD1012 g) (Went 1960). Since that seminal study, estimates of global BVOC emissions (excluding methane) have been refined through coupled vegetation– atmosphere models and better maps of global vegetation. Currently, the worldwide emissions are estimated to be around 1 Pg C year1 (1 PgD1015 g) (Guenther et al. 2012). Much of the past research on plant volatile emissions has been, and continues to be, on the simple C5 volatile hydrocarbon, isoprene, which is emitted from leaves in a light- and temperature-dependent manner and is coupled to the metabolic processes of photosynthesis (Sanadze 1956; Rasmussen and Went 1965; Rasmussen 1970). Since its initial discovery, the research on biogenic isoprene has focused on understanding its source strength and distribution among different plant taxa, resulting in the construction of first list of isoprene-emitting plants (Rasmussen 1978) and first biogenic emission inventory system (BEIS, Pierce and Waldruff 1991), followed by more biologically oriented emission algorithms and inventories (e.g., Guenther et al. 1991, 1994, 2006, 2012; Arneth et al. 2007; Monson et al. 2012). By now, it is widely acknowledged that multiple plant BVOC emissions play a major role in atmospheric dynamics within the Earth system with highly reactive compounds reacting in the gas phase to affect atmospheric chemistry, including influences on less reactive compounds that affect the atmosphere’s global warming potential, e.g., methane (Fuentes et al. 2000).
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