Emissions of monoterpenes linalool and ocimene respond differently to environmental changes due to differences in physico-chemical characteristics

We investigated the 13C-labeling kinetics of the emission of two major monoterpenes emitted by needles of Mediterranean conifer Pinus pinea L., monoterpene alcohol linalool and non-oxygenated monoterpene trans-β-ocimene. These data were further used to develop and parameterize a dynamics monoterpene emission model, predicting the emissions of monoterpenes with contrasting physico-chemical properties to environmental changes. All monoterpenes emitted were labeled by 13C in short pulse-labeling experiments. 13C-labeling experiments further indicated for these two monoterpenes comprising 77% of total emissions that a major part of the emissions of these two monoterpenes relied on recently synthesized carbon not on specific storage compartments within the resin ducts. However, labeling kinetics suggested existence of transient storage pools, located within the needle aqueous and lipid phases. For linalool, we found half-lives of 13 min for the aqueous phase storage and 3 h for the lipid phase while trans-β-ocimene exhibit an aqueous phase half-life of 2 and 15 min for the lipid phase, overall indicating that the transient storage due to limited monoterpene volatility can significantly alter the emission dynamics. The key physico-chemical characteristics determining the time constants of the transient storage pools were the Henryʹs law constant (liquid/gas phase partition coefficient) and the octanol/water (lipid/liquid) phase partition coefficient. As monoterpene Henryʹs law constants vary over four orders of magnitude and octanol/water partition coefficients over three orders of magnitude, the capacity for non-specific storage, and damping of the effects of rapidly changing environmental conditions is expected to strongly vary among different monoterpenes. Overall, our study suggests that non-specific storage due to limited volatility is a common phenomenon of common of plant-emitted compounds.