LAUSR

BACKGROUND AND AIMS Polyploidization can improve plant mass yield for bioenergy support, yet few studies have investigated ozone (O3) sensitivity linked to internal regulatory mechanism at different ploidy levels. METHODS Diploid and triploid Populus tomentosa Carr. plants were exposed to ambient and ambient plus 60 ppb [O3]. We explored their differences in sensitivity (leaf morphological, physiological and biochemical traits, and plant mass) as well as mechanisms of avoidance (stomatal conductance, xanthophyll cycle, thermal dissipation) and tolerance (ROS scavenging system) in response to O3 at two developmental phases. KEY RESULTS Triploid plants had the highest plant growth under ambient O3, even under O3 fumigation. However, triploid plants were the most sensitive to O3 and under elevated O3 showed the largest decreases in photosynthetic capacity and performance, as well as increased shoot to root ratio, and the highest lipid peroxidation. Thus, plant mass production could be impacted in triploid plants under long-term O3 contamination. Both diploid and triploid plants reduced stomatal aperture in response to O3, thereby reducing O3 entrance, yet only in diploid plants was reduced stomatal aperture associated with minimal (non-significant) damage to photosynthetic pigments and lower lipid peroxidation. CONCLUSIONS Tolerance mechanisms of plants of both ploidy levels mainly focused on the enzymatic reduction of hydrogen peroxide through hydrogen peroxidase (CAT) and peroxidase (POD), yet those homeostatic regulatory mechanisms were higher in diploid plants. Our study recommends triploid white poplar as a bioenergy species only under short term O3 contamination. Under continuously elevated O3 over the long term, diploid white poplar may perform better.