Evaluation of O3 Effects on Cumulative Photosynthetic CO2 Uptake in Seedlings of Four Japanese Deciduous Broad-Leaved Forest Tree Species Based on Stomatal O3 Uptake

Abstract

The current level of tropospheric ozone (O3) is expected to reduce the net primary production of forest trees. Here, we evaluated the negative effects of O3 on the photosynthetic CO2 uptake of Japanese forest trees species based on their cumulative stomatal O3 uptake, defined as the phytotoxic O3 dose (POD). Seedlings of four representative Japanese deciduous broad-leaved forest tree species (Fagus crenata, Quercus serrata, Quercus mongolica var. crispula and Betula platyphylla var. japonica) were exposed to different O3 concentrations in open-top chambers for two growing seasons. The photosynthesis–light response curves (A-light curves) and stomatal conductance were measured to estimate the leaf-level cumulative photosynthetic CO2 uptake (ΣPn_est) and POD, respectively. The whole-plant-level ΣPn_est were highly correlated with the whole-plant dry mass increments over the two growing seasons. Because whole-plant growth is largely determined by the amount of leaf area per plant and net photosynthetic rate per leaf area, this result suggests that leaf-level ΣPn_est, which was estimated from the monthly A-light curves and hourly PPFD, could reflect the cumulative photosynthetic CO2 uptake of the seedlings per unit leaf area. Although the O3-induced reductions in the leaf-level ΣPn_est were well explained by POD in all four tree species, species-specific responses of leaf-level ΣPn_est to POD were observed. In addition, the flux threshold appropriate for the linear regression of the responses of relative leaf-level ΣPn_est to POD was also species-specific. Therefore, species-specific responses of cumulative photosynthetic CO2 uptake to POD could be used to accurately evaluate O3 impact on the net primary production of deciduous broad-leaved trees.

Impact Assessment of Ozone Absorbed through Stomata on Photosynthetic Carbon Dioxide Uptake by Japanese Deciduous Forest Trees: Implications for Ozone Mitigation Policies

“…However, this has not been clarified to date. In the present study, therefore, we assumed that the responses of CO2 uptake to COU obtained in the seedlings in Yamaguchi et al [18] were the same as those in the mature trees, although this might cause estimation errors in the impact of O3 on CO2 uptake to some extent. Responses of annual CO2 uptake per unit leaf area to cumulative stomatal O3 uptake (COU) of F. crenata, Q. serrata, Q. mongolica var.…”

“…Third, COU in the tree distribution areas (Ministry of the Environment, http://www.biodic.go.jp/index.html) was estimated by interpolating the COU at the monitoring stations of O 3 using ordinary kriging. Fourth, according to species-specific responses of annual CO 2 uptake to COU reported by Yamaguchi et al [18], O 3 -induced reductions in CO 2 uptake for the four trees were calculated. Finally, the effects of O 3 mitigation, i.e., impact of reducing the surface O 3 concentration, on CO 2 uptake were calculated for the four tree species by simulating the input O 3 concentrations.…”

“…where ω and λ are species-specific parameters of the Weibull function. ω and λ were originally proposed by Yamaguchi et al [18] and were modified to make the intercept 100 ( Figure 2). The gaussian model was used as a semi-variogram model in the ordinary kriging to interpolate the annual COU at the O 3 monitoring stations, which was clipped by the tree distribution.…”

“…where ω and λ are species-specific parameters of the Weibull function. ω and λ were originally proposed by Yamaguchi et al [18] and were modified to make the intercept 100 ( Figure 2). Since previous studies indicated that leaf morphological and physiological characteristics, such as leaf mass per area and gross photosynthetic rate, are related to the sensitivity to O3 [7,25], the leaflevel photosynthetic sensitivity to O3 might be different between seedlings and mature trees due to the differences in their leaf characteristics.…”

“…Recently, Yamaguchi et al [18] evaluated the species-specific responses of cumulative photosynthetic CO 2 uptake to COU of the leaves in four Japanese forest tree species: F. crenata, Q. serrata, Q. mongolica var. crispula, and B. platyphylla var.…”