Ozone exposure affects leaf wettability and tree water balance

Relatively little is known about the influences of growing-season backgroun d ozone (O-3) concentrations on leaf cuticles and foliar water loss. Using fumigation chambers, leaf wettability and foliar water loss were stud ied in two poplar species, Populus nigra and P. euramericana, and a conifer , Pseudotsuga menziesii, under three O-3 regimes; control (approx. 1 ppbv O -3), urban O-3, exposure (13-41 ppbv O-3), and montane O-3 exposure (30-45 ppbv O-3). Urban O-3 exposure delayed a decrease in droplet contact angles overtime in Populus leaves by 2-4 wk, and decreased droplet contact angles of P. menzi esii foliage. Ozone exposure increased foliar water loss and minimal conduc tance to water vapour for P. euramericana, but not P. nigra and P. menziesi i. Both Populus species had lower photosynthetic biomass in O-3 treatments, due to production of fewer new leaves, premature leaf abscission and decre ased leaf size (P. euramericana only). Leaf abscission was preceded by foli ar injury symptoms characteristic of O-3 exposure. Results suggest that exposure to [O-3] common during the growing season can increase water loss in Populus saplings, but this effect might be offset b y decreased foliar biomass. Importantly, responses were highly species spec ific in a given O-3 treatment.