Abstract

Photosynthesis by trees is expected to contribute to preventing climate change including global warming. However, the current levels of tropospheric ozone (O3) reduce the uptake of photosynthetic carbon dioxide (CO2) by forest trees in Japan, which is a concern. Furthermore, it is unknown how much O3 should be reduced to prevent plants’ O3-induced damage. The objective of the present study was to assess the negative effects of the current levels of O3 absorbed via stomata and the impact of its mitigation on the CO2 uptake by trees in Japanese forests. Impact assessment, targeted in 2011–2015, was performed for four deciduous broad-leaved trees: Fagus crenata, Quercus serrata, Q. mongolica var. crispula, and Betula platyphylla var. japonica. The assessment was based on species-specific cumulative stomatal O3 uptake (COU) and species-specific responses of annual photosynthetic CO2 uptake to COU. Annual COU differed between the four trees; the average COU of F. crenata, Q. serrata, Q. mongolica var. crispula, and B. platyphylla var. japonica across Japan was 41.7, 26.5, 33.0, and 29.1 mmol m−2, respectively, and the reductions in CO2 uptake by the four trees were 14.0%, 10.6%, 8.6%, and 15.4%, respectively. Further analysis revealed that reducing the atmospheric O3 concentration by approximately 28%, 20%, 17%, and 49% decreased the O3-induced reductions in photosynthetic CO2 uptake to 5% in F. crenata, Q. serrata, Q. mongolica var. crispula, and B. platyphylla var. japonica, respectively. In the near future, implementing mitigation measures for the O3 damage in plants is expected to enhance the photosynthetic capacity of Japanese forest tree species.

Highlights

  • Climate change, including rising air temperatures and changes in precipitation, is recognized globally as a serious environmental problem [1]

  • The present study firstly evaluated the impact of the current levels of O3 absorbed via stomata on the annual cumulative photosynthetic CO2 uptake per unit leaf area of four Japanese forest tree species

  • The O3 -induced reduction in annual CO2 uptake averaged across Japan was 14.0%, 10.6%, 8.6%, and 15.4% in F. crenata, Q. serrata, Q. mongolica var. crispula, and B. platyphylla var. japonica, respectively (Figures 5 and 6)

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Summary

Introduction

Climate change, including rising air temperatures and changes in precipitation, is recognized globally as a serious environmental problem [1]. Atmospheric carbon dioxide (CO2 ) is one of the major factors causing climate change [1]. Forests 2020, 11, 137 μmol mol−1 (ppm) from 280 ppm in 1750 with the increasing consumption of fossil fuels and burning of biomass [2,3]. Forest trees absorb atmospheric CO2 by leaf photosynthesis, which is expected to attenuate climate change [4,5,6]. Tropospheric ozone (O3 ) exhibits direct radiative forcing for climate change [1]. O3 has a potential for indirect radiative forcing, as it reduces the photosynthetic CO2 uptake because of its high phytotoxicity [7,8]. Sitch et al [9] suggested that indirect radiative forcing, which is the O3 -induced reduction in the photosynthetic CO2 fixation, could contribute to global warming. An impact assessment of O3 on photosynthetic CO2 uptake is needed to support countermeasures, such as adaptation and mitigation, against the detrimental impact of O3

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