Atmospheric CO2 Concentration and N Availability Affect the Balance of the Two Photosystems in Mature Leaves of Rice Plants Grown at a Free-Air CO2 Enrichment Site

Hiroshi Ozaki; Takeshi Tokida; Hirofumi Nakamura; Hidemitsu Sakai; Toshihiro Hasegawa; Ko Noguchi

doi:10.3389/fpls.2020.00786

Atmospheric CO₂ Concentration and N Availability Affect the Balance of the Two Photosystems in Mature Leaves of Rice Plants Grown at a Free-Air CO₂ Enrichment Site

Front Plant Sci. 2020 Jun 9:11:786. doi: 10.3389/fpls.2020.00786. eCollection 2020.

Authors

Hiroshi Ozaki¹, Takeshi Tokida², Hirofumi Nakamura³, Hidemitsu Sakai⁴, Toshihiro Hasegawa⁵, Ko Noguchi¹

Affiliations

¹ School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, Hachioji, Japan.
² Division of Biogeochemical Cycles, Institute for Agro-Environmental Sciences, Tsukuba, Japan.
³ Taiyo Keiki Co., Ltd., Toda, Japan.
⁴ Division of Climate Change, Institute for Agro-Environmental Sciences, Tsukuba, Japan.
⁵ Division of Agro-Environmental Research, Tohoku Agricultural Research Center, Morioka, Japan.

Abstract

Atmospheric CO₂ concentration ([CO₂]) has been substantially increasing. Responses of leaf photosynthesis to elevated [CO₂] have been intensively investigated because leaf photosynthesis is one of the most important determinants of crop yield. The responses of photosynthesis to elevated [CO₂] 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 [CO₂] and N levels, and thus to clarify if responses of photosynthetic electron transport rates (ETRs) of the two photosystems to elevated [CO₂] are altered by N availability. Thus, we examined parameters of the two photosystems in mature leaves of rice plants grown under two [CO₂] levels (ambient and 200 μmol mol^-1 above ambient) and three N fertilization levels at the Tsukuba free-air CO₂ enrichment experimental facility in Japan. Responses of ETR of PSII (ETRII) and ETR of PSI (ETRI) to [CO₂] levels differed among N levels. When moderate levels of N were applied (MN), ETRI was higher under elevated [CO₂], whereas at high levels of N were applied (HN), both ETRII and ETRI were lower under elevated [CO₂] compared with ambient [CO₂]. Under HN, the decreases in ETRII and ETRI under elevated [CO₂] 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 [CO₂] 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 [CO₂] 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.

Keywords: CO2 enrichment; FACE; nitrogen; photosystem I; photosystem II; rice (Oryza sativa).