Fig. 2.

Example of the experimental routine of the leaf wounding experiment demonstrating changes in induced emissions of (a) acetaldehyde measured by a proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS) with 1 s resolution, (b) apparent stomatal conductance and (c) net assimilation rate, and (d) alterations in constitutive isoprene emission rate in Populus tremula. The data presented correspond to a 15 mm razor cut through the leaf lamina. In (a), the raw recorded data are shown by a grey line and the smoothed data by a continuous line. The reference baseline is an average of the reference measurement period prior to the leaf wounding. The ‘missing data period’ corresponds to the time where the leaf had to be removed from the chamber to perform the mechanical damage at time zero as well as the unreliable data recording during the stabilization of gas flow. The raw data of the emission peak was fitted to a Gaussian function. The extrapolation of the fitting to time zero corresponding to the missing data period is represented with a dashed line. The inset in (a) illustrates the procedure to determine the maximum slope of volatile organic compound emission. The dashed line (left y-axis) is the Gaussian fit, and the solid line (right y-axis) is the first derivative of the data.