Effects of ozone-induced stomatal closure on ozone uptake and its changes due to leaf age in sun and shade leaves of Siebold's beech

Abstract

An estimation of stomatal ozone uptake for the assessment of ozone risks in forest trees can be modified by ozoneinduced stomatal closure. We thus examined a seasonal course of stomatal conductance in sun and shade leaves of Siebold’s beech native to northern Japan (Fagus crenata) grown under free-air ozone exposure. A performance of multiplicative stomatal conductance model was also tested, when considering ozone-induced stomatal closure into the model. Ozone caused stomatal closure in both sun and shade leaves (20% and 30–40% reduction of stomatal conductance in sun and shade leaves, respectively) during early summer. However, in autumn, stomatal closure was diminished regardless of canopy positions (approximately 7% and 6% reduction of stomatal conductance in sun and shade leaves, respectively). When observed seasonal course of stomatal closure was taken into account in stomatal conductance model, the model provided a good agreement with measurements even under conditions of elevated ozone. As a result, ozone-induced stomatal closure limited stomatal ozone uptake by 11% and 17% in sun and shade leaves of Siebold’s beech, respectively. In addition, stomatal ozone uptake in shade leaves under elevated ozone was much less than that in sun leaves (35% of the value in sun leaves), indicating better avoidance of ozone stress in shade leaves. Our results suggest that a loss of ozoneinduced stomatal closure after ozone exposure in the late growing season should be considered in modeling stomatal ozone uptake for the assessment of ozone impacts on Siebold’s beech.