Paper Reviewed
Hiraoka, Y., Mine Nose, T.I., Tobita, H., Yazaki, K., Watanabe, A., Fujisawa, Y. and Kitao, M. 2017. Species characteristics and intraspecific variation in growth and photosynthesis of Cryptomeria japonica under elevated O3 and CO2. Tree Physiology 37: 733-743.

Japanese cedar (Cryptomeria japonica) is a key silviculture species in Japan, making up approximately 44 percent of the country's plantation area. Given such prominence, Hiraoka et al. write that "in order to adapt to future environments, tree improvement programs will need to consider rising O3 and CO2 concentrations, as well as other changes in climate" that may occur. Therefore, as their contribution to this effort, the team of seven Japanese researchers investigated the individual and combined impacts of carbon dioxide (CO2) and ozone (O3) on the growth of Japanese cedar.

To accomplish their goal, they planted 1-year-old cuttings from twelve C. japonica clones in a free-air CO2 enrichment (FACE) facility at the Forestry and Forest Products Research Institute in Tsukuba, Japan. The trees were grown for two years under one of four treatment conditions during the growing season: (1) ambient air, (2) twice-ambient O3 (approximately +30 ppb), (3) elevated CO2 (~550 ppm during daylight hours) and (4) twice-ambient O3 and elevated CO2. During the experiment, as well as at its end, the scientists made a number of measurements to discern the impacts of the different treatments on the growth of the young trees.

Results of their analysis revealed that C. japonica had a low sensitivity to the negative (growth-retarding) effects of O3. In fact, as illustrated in the figure below, trees growing in the elevated O3 environment had higher plant dry mass than their ambient counterparts, though the difference were not statistically significant. With respect to elevated CO2, it induced a statistically significant increase in stem, shoot, root and total plant biomass (see figure below), the latter of which parameter increased by some 60 percent in response to a relatively small CO2 stimulation of approximately 175 ppm. Tree dry mass was also improved in the combined elevated O3 and elevated CO2 treatment, though not quite to the extent as it was in the CO2 treatment alone. Consequently, in light of all of the above, it would appear that Japanese cedar growth will experience enhancements in the years and decades to come as both the CO2 and O3 contents of the atmosphere increase. And that is great news for the silviculture industry in Japan.

Figure 1. Average stem (a), lateral shoot (b), root (c) and whole plant dry mass (d) of 3-yr-old Cryptomeria japonica trees at the end of a 2-year CO2 and O3 experiment. Shaded colors indicate the treatment regime. Asterisks indicate significant differences between ambient and other treatments by Dunnett's test; P < 0.05. Error bars represent the 95% confidence interval. Adapted from Hiraoka et al. (2017).