Environmental and physiological controls on diurnal and seasonal patterns of biogenic volatile organic compound emissions from five dominant woody species under field conditions.

Biogenic volatile organic compounds (BVOCs) play essential roles in tropospheric chemistry, on both regional and global scales. The emissions of large quantities of species-specific BVOC depend not only on environmental (temperature, T; photosynthetically active radiation, PAR), but also physiological parameters (i.e. net photosynthetic rate, P_n; transpiration rate, T_r; stomatal conductance, g_s and intercellular CO₂ concentration, C_i). Here, isoprene, monoterpene and sesquiterpene emissions were determined from five dominant mature woody tree species in northern China, which are two evergreen conifers (Pinus tabuliformis and Platycladus orientalis) and three broad-leaved deciduous trees (Quercus variabilis, Populus tomentosa and Robinia pseudoacacia). A dynamic enclosure technique combined with GC-MS was used to sample BVOCs and analyse their fractional composition at daily and annual scales. The diurnal data showed that both isoprene and monoterpene emissions increased with increasing temperature, and reached their maximum emission rates in the peak of growing season for both coniferous and broad-leaved species. The emissions of individual compound within the monoterpenes and sesquiterpenes were statistically correlated with each other for all species. Furthermore, some oxygenated monoterpene emissions were highly correlated to sesquiterpenes in all tree species. Linking BVOC emissions to environmental and leaf physiological parameters exhibited that monoterpene emissions were linearly and positively correlated to the variation of T, PAR, P_n and T_r, while their relationship to g_s and C_i is more complex. Collectively, these findings provided important information for improving current model estimations in terms of the linkage between BVOC emissions and plant physiological traits. The data presented in this study can be used to update emission capacity used in models, as this is the first time of reporting BVOC emissions from five dominant species in this region. The whole-year measurement of leaf-level BVOCs can also advance our understanding of seasonal variation in BVOC emissions.