Photosynthesis of three evergreen broad-leaved tree species, Castanopsis sieboldii, Quercus glauca, and Q. myrsinaefolia, under elevated ozone

The main goal of this study was to obtain detailed information on photosynthetic responses of evergreen broad-leaved tree species to ozone (O3). For this, two-year-old seedlings of Castanopsis sieboldii, Quercus glauca, and Q. myrsinaefolia were grown for one growing season, from 15 May to 27 October 2014 under three levels of gas treatments, charcoal-filtered air and 1.0 time and 1.5 times ambient O3 concentrations. We analysed the intercellular CO2 concentration-response curve of the net photosynthetic rate, i.e., the A/Ci curve, in July and October, and growth measurement was carried out at the end of the experiment in October. We observed a difference in O3 susceptibility among the species. Negative effects of O3 were observed on the growth and photosynthetic traits of C. sieboldii, while no significant effects on these traits were noted in the two Quercus species. The decrease in light-saturated net photosynthetic rate (Asat) of C. sieboldii under elevated O3 was accompanied with a significant decrease in the maximum rate of carboxylation (Vcmax). Decreases of leaf nitrogen content and nitrogen use efficiency to Rubisco are considered as factors contributing to lower Vcmax in C. sieboldii seedlings under elevated O3. In addition to the decrease in Vcmax, O3 exposure induced marginal increase of stomatal limitation of photosynthesis. These results indicate that both biochemical and diffusion processes in photosynthesis are responsible for the decrease in Asat of C. sieboldii under elevated O3.