Seasonal variation of isoprene basal emission in mature Quercus crispula trees under experimental warming of roots and branches

163 Guenther et al., 2006) which models the effects of changing phenological and environmental variables on isoprene and other BVOC given species-specific basal emission rates. The isoprene basal emission rate is defined as a constant emission factor representing the capacity of a given plant species to emit isoprene under standard environmental conditions (30°C, 1000 μmol m–2 s–1 of photosynthetic photon flux density (PPFD)). It is known that the basal emission rate of isoprene can be altered by the physiology of the plant, growth stage of leaves, etc. (Monson et al., 1994; Xiaoshan et al., 2000). Previous experimental studies have shown that isoprene basal emissions generally increase with increasing temperatures (e.g., Pétron et al., 2001). This temperature response has also been analyzed by comparing emission rates across different seasons (after accounting for differences in light and temperature) (e.g., Monson et al., 1994) or by using potted plants exposed to different temperatures in greenhouses (e.g., Pétron et al., 2001). To our knowledge, no experiments have been performed to date in the mature oak canopies of Japan despite the fact that oaks are the dominant isoprene-emitting trees in JaSeasonal variation of isoprene basal emission in mature Quercus crispula trees under experimental warming of roots and branches