Temperature and light dependency of isoprene and monoterpene emissions from tropical and subtropical trees: Field observations in south China

Temperature and light are the two most important parameters regulating emissions of biogenic volatile organic compound (BVOC) from plant leaves, yet few field campaigns have been conducted to investigate the light and temperature dependency of BVOC emissions from tropical/subtropical trees. In this study, branch-scale emissions of isoprene and monoterpenes from typical tree species were measured using a dynamic plant chamber in the Pearl River Delta (PRD) region in south China. Our results showed that the temperature- and light-dependent isoprene emissions from the investigated trees could be well captured by the algorithms proposed by Guenther et al. (1993) (G93). However, the previously reported temperature-dependent algorithm for monoterpene emissions with a constant or fitted scaling β factor, could not well simulate monoterpene emissions from the tropical/subtropical trees. The temperature- and light-dependent G93 algorithm for isoprene instead could simulate the monoterpene emissions fairly well, indicating that the emissions of monoterpenes from tropical/subtropical trees depended on both temperature and light like that of isoprene, and that monoterpenes were directly emitted after biosynthesis without storing. This emission pattern was similar to that previously reported for some tropical trees, but different from most temperate and boreal trees. Moreover, when pooling together the measured data of all trees, observed emission rates (normalized to E_s) and the G93 predicted values (normalized to E_s) showed highly significant linear correlations for both isoprene (slope = 0.92; r² = 0.95) and monoterpenes (slope = 0.95; r² = 0.95). The result indicates that the emission model in the tropical/subtropical regions could potentially be simplified to use the G93 isoprene algorithm to formulate both isoprene and monoterpene emissions.