Controls on the emission of plant volatiles through stomata: A sensitivity analysis

According to experimental studies, plant emissions of volatile organic compounds (VOC) are controlled by stomata to a varying extent, but the differing responses could not be explained so far. A dynamic emission model developed in a previous study indicated that stomata may limit the emission rate in a nonsteady state conditions, whereas the rate of increase of liquid‐phase volatile concentrations controls the degree to which stomata temporarily curtail the emission. Despite its large predictive capability, potentially large number of volatile physico‐chemical and leaf structural variables are needed for parameterization of such dynamic models, limiting the usefulness of the approach. We conducted a sensitivity analysis to determine the effect of varying VOC distribution between gas‐ and liquid‐phases (Henry's law constant, H , Pa m 3 mol −1 ) and varying internal diffusion conductances in the liquid‐ and gas‐phases. The model was parameterized for three contrasting leaf architectures (conifer, sclerophyll, and mesophytic leaves). The sensitivity analysis indicated that the volatile H value is the key variable affecting the stomatal sensitivity of VOC emissions. Differences in leaf architecture, in particular in leaf liquid volume to area ratio, also modified the emission responses to changes in stomatal aperture, but these structural effects were superimposed by compound gas/liquid phase partitioning. The results of this analysis indicate that major effort in parameterization of dynamic VOC emission models should be directed toward obtaining reliable gas/liquid‐phase equilibria for various plant volatiles, and that these models may readily be applied for leaves with contrasting architecture.