Ozaki Hiroshi, Tokida Takeshi, Nakamura Hirofumi, Sakai Hidemitsu, Hasegawa Toshihiro, Noguchi Ko
School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, Hachioji, Japan.
Division of Biogeochemical Cycles, Institute for Agro-Environmental Sciences, Tsukuba, Japan.
Front Plant Sci. 2020 Jun 9;11:786. doi: 10.3389/fpls.2020.00786. eCollection 2020.
Atmospheric CO concentration ([CO]) has been substantially increasing. Responses of leaf photosynthesis to elevated [CO] have been intensively investigated because leaf photosynthesis is one of the most important determinants of crop yield. The responses of photosynthesis to elevated [CO] can depend on nitrogen (N) availability. Here, we aimed to investigate the significance of the appropriate balance between two photosystems [photosystem I (PSI) and photosystem II (PSII)] under various [CO] and N levels, and thus to clarify if responses of photosynthetic electron transport rates (ETRs) of the two photosystems to elevated [CO] are altered by N availability. Thus, we examined parameters of the two photosystems in mature leaves of rice plants grown under two [CO] levels (ambient and 200 μmol mol above ambient) and three N fertilization levels at the Tsukuba free-air CO enrichment experimental facility in Japan. Responses of ETR of PSII (ETRII) and ETR of PSI (ETRI) to [CO] levels differed among N levels. When moderate levels of N were applied (MN), ETRI was higher under elevated [CO], whereas at high levels of N were applied (HN), both ETRII and ETRI were lower under elevated [CO] compared with ambient [CO]. Under HN, the decreases in ETRII and ETRI under elevated [CO] were due to increases in the non-photochemical quenching of PSII [Y(NPQ)] and the donor side limitation of PSI [Y(ND)], respectively. The relationship between the effective quantum yields of PSI [Y(I)] and PSII [Y(II)] changed under elevated [CO] and low levels of N (LN). Under both conditions, the ratio of Y(I) to Y(II) was higher than under other conditions. The elevated [CO] and low N changed the balance of the two photosystems. This change may be important because it can induce the cyclic electron flow around PSI, leading to induction of non-photochemical quenching to avoid photoinhibition.
大气中二氧化碳浓度（[CO]）一直在大幅增加。由于叶片光合作用是作物产量最重要的决定因素之一，因此对叶片光合作用对升高的[CO]的响应进行了深入研究。光合作用对升高的[CO]的响应可能取决于氮（N）的有效性。在这里，我们旨在研究在不同的[CO]和N水平下两个光系统[光系统I（PSI）和光系统II（PSII）]之间适当平衡的重要性，从而阐明两个光系统的光合电子传递速率（ETR）对升高的[CO]的响应是否会因N的有效性而改变。因此，我们在日本筑波自由空气CO富集实验设施中，研究了在两种[CO]水平（环境水平和比环境水平高200 μmol mol）和三种氮肥水平下生长的水稻植株成熟叶片中两个光系统的参数。PSII的ETR（ETRII）和PSI的ETR（ETRI）对[CO]水平的响应在不同N水平之间存在差异。当施用中等水平的N（MN）时，在升高的[CO]条件下ETRI较高，而当施用高水平的N（HN）时，与环境[CO]相比，在升高的[CO]条件下ETRII和ETRI均较低。在HN条件下，升高的[CO]条件下ETRII和ETRI的降低分别是由于PSII的非光化学猝灭[Y（NPQ）]增加和PSI的供体侧限制[Y（ND）]增加所致。在升高的[CO]和低水平的N（LN）条件下，PSI的有效量子产率[Y（I）]和PSII的有效量子产率[Y（II）]之间的关系发生了变化。在这两种条件下，Y（I）与Y（II）的比值均高于其他条件。升高的[CO]和低N改变了两个光系统的平衡。这种变化可能很重要，因为它可以诱导围绕PSI的循环电子流，导致非光化学猝灭的诱导以避免光抑制。
