The hydrocarbon emission rates of tea-leafed willow (Salix phylicifolia), silver birch (Betula pendula) and European aspen (Populus tremula)

The monoterpene, isoprene, and light hydrocarbon emission rates of tea-leafed willow (Salix phylicifolia), aspen (Populus tremula), and silver birch (Betula pendula) were measured during the growing season 1996 in the boreal vegetation zone using a dynamic flow-through technique. All tree species had significant (2.8–10 μg g (dry weight)-1 h-1) monoterpene emission rates when leaves were young in May. In addition, willow emitted 1-butene, ethene, and propene when it was blooming in May. In August, silver birch emitted monoterpenes (6–12 μg g (dry weight)-1 h-1). Then the main species emitted were ocimenes and sabinene. Birch emitted only minor amounts of isoprene. Willow and aspen are high isoprene emitters (up to 76 μg g (dry weight)-1 h-1 in August). Isoprene emissions began 2–3 weeks after onset of leafing. The phenological state was estimated using the effective temperature sum. Isoprene synthase began when the effective temperature sum exceeded 120–210 and 120–280 degree days for willow and aspen, respectively. In addition to phenology, isoprene emissions were dependent on temperature and photosynthetically active radiation while the terpene emissions were dependent on temperature only.