Estimates of Isoprene and Monoterpene Emission Rates in Plants

Abstract

A range of plant species, including crops, shrubs, herbs, and trees, was surveyed to determine the magnitude of isoprene emissions. In studies to determine if plants emitted isoprene, greenhouse-grown plants were encapsulated in impermeable plastic bags and kept in a growth chamber for 2 h at 30 C and a photosynthetic photon flux density of ca. 350 μE m-2 s-1. To estimate emission rates, greenhouse-grown plants were conditioned in a growth chamber and transferred to a controlled-environment gas-exchange chamber. Gas samples from either the encapsulation bags or gas-exchange chamber were collected, concentrated cryogenically, and analyzed by gas-liquid chromatography. The occurrence of isoprene and monoterpenes was confirmed by combined gas chromatography-mass spectrometry. Of the 54 plant species tested, 37 emitted isoprene. Isoprene emission rates (28 C and 1,000 μE m-2 s-1) for 16 species ranged from 0 to 38.5 μg carbon g-1 h-1. Monoterpenes were detected from six species and emission rates ranged from 0.01 to 3.53 μg carbon g-1 h-1. The encapsulation technique permitted rapid identification of species that emitted isoprene. The emission rate data confirmed the preliminary isoprene ranking and demonstrated the differences between monoterpene and isoprene emissions.