Species characteristics and intraspecific variation in growth and photosynthesis of Cryptomeria japonica under elevated O 3 and CO 2

In order to predict the effects of future atmospheric conditions on forest productivity, it is necessary to clarify the physiological responses of major forest tree species to high concentrations of ozone (O 3) and carbon dioxide (CO 2). Furthermore, intraspecific variation of these responses should also be examined in order to predict productivity gains through tree improvements in the future. We investigated intraspecific variation in growth and photosynthesis of Cryptomeria japonica D. Don, a major silviculture species in Japan, in response to elevated concentrations of O 3 (eO 3) and CO 2 (eCO 2), separately and in combination. Cuttings of C. japonica were grown and exposed to two levels of O 3 (ambient and twice-ambient levels) in combination with two levels of CO 2 (ambient and 550 μmol mol '1 in the daytime) for two growing seasons in a free-air CO 2 enrichment experiment. There was no obvious negative effect of eO 3 on growth or photosynthetic traits of the C. japonica clones, but a positive effect was observed for annual height increments in the first growing season. Dry mass production and the photosynthetic rate increased under eCO 2 conditions, while the maximum carboxylation rate decreased. Significant interaction effects of eO 3 and eCO 2 on growth and photosynthetic traits were not observed. Clonal effects on growth and photosynthetic traits were significant, but the interactions between clones and O 3 and/or CO 2 treatments were not. Spearman's rank correlation coefficients between growth traits under ambient conditions and for each treatment were significantly positive, implying that clonal ranking in growth abilities might not be affected by either eO 3 or eCO 2. The knowledge obtained from this study will be helpful for species selection in afforestation programs, to continue and to improve current programs involving this species, and to accurately predict the CO 2 fixation capacity of Japanese forests.