Light Energy Partitioning under Various Environmental Stresses Combined with Elevated CO2 in Three Deciduous Broadleaf Tree Species in Japan

Mitsutoshi Kitao,Takayoshi Koike,Hisanori Harayama,Evgenios Agathokleous,Hiroyuki Tobita,Kenichi Yazaki,Masabumi Komatsu,Satoshi Kitaoka

doi:10.3390/cli7060079

Abstract

Understanding plant response to excessive light energy not consumed by photosynthesis under various environmental stresses, would be important for maintaining biosphere sustainability. Based on previous studies regarding nitrogen (N) limitation, drought in Japanese white birch (Betula platyphylla var. japonica), and elevated O3 in Japanese oak (Quercus mongolica var. crispula) and Konara oak (Q. serrata) under future-coming elevated CO2 concentrations, we newly analyze the fate of absorbed light energy by a leaf, partitioning into photochemical processes, including photosynthesis, photorespiration and regulated and non-regulated, non-photochemical quenchings. No significant increases in the rate of non-regulated non-photochemical quenching (JNO) were observed in plants grown under N limitation, drought and elevated O3 in ambient or elevated CO2. This suggests that the risk of photodamage caused by excessive light energy was not increased by environmental stresses reducing photosynthesis, irrespective of CO2 concentrations. The rate of regulated non-photochemical quenching (JNPQ), which contributes to regulating photoprotective thermal dissipation, could well compensate decreases in the photosynthetic electron transport rate through photosystem II (JPSII) under various environmental stresses, since JNPQ+JPSII was constant across the treatment combinations. It is noteworthy that even decreases in JNO were observed under N limitation and elevated O3, irrespective of CO2 conditions, which may denote a preconditioning-mode adaptive response for protection against further stress. Such an adaptive response may not fully compensate for the negative effects of lethal stress, but may be critical for coping with non-lethal stress and regulating homeostasis. Regarding the three deciduous broadleaf tree species, elevated CO2 appears not to influence the plant responses to environmental stresses from the viewpoint of susceptibility to photodamage.

Highlights

Light is essential for plant growth, plants can suffer from excessive light, especially when combined with other environmental stresses
When photosynthetic electron transport is suppressed under environmental stresses, an increase in the fraction of non-regulatory, non-photochemical quenching suggests that plants cannot fully dissipate excess energy through a regulated process [5,6,7,8,9]
Non-regulated, non-photochemical quenching can be a measure of oxidative stress, as the level of lipid peroxidation indicated by malondialdehyde (MDA) accumulation was closely correlated with the quantum yield of non-regulated, non-photochemical quenching (Y(NO)) in Arabidopsis thaliana under a water deficit imposed by withholding the water supply [17]

Summary

Introduction

Light is essential for plant growth, plants can suffer from excessive light, especially when combined with other environmental stresses. Absorbed light energy is dissipated by non-photochemical processes divided into two parts: Constitutive, non-regulatory, non-photochemical quenching, and regulatory light-induced, non-photochemical quenching [2,3,4,5]. When photosynthetic electron transport is suppressed under environmental stresses, an increase in the fraction of non-regulatory, non-photochemical quenching suggests that plants cannot fully dissipate excess energy through a regulated process [5,6,7,8,9]. Non-regulated, non-photochemical quenching consists of chlorophyll fluorescence internal conversions and intersystem crossing, which leads to the formation of 1 O2 via the triplet state of chlorophyll (3 chl*) [10,11,12,13]. Non-regulated, non-photochemical quenching consists of chlorophyll fluorescence internal conversions and intersystem crossing, which leads to the formation of 1 O2 via the triplet state of chlorophyll (3 chl*) [10,11,12,13]. 1 O2 can lead to PSII photodamage directly, or via inhibiting PSII repair processes [14,15,16].

Methods

Results

Discussion

Conclusion