Multiyear CO2 elevation improves PSII efficiency in a japonica rice cultivar

Abstract Responses of crop photosystem activity to the short‐term elevation of carbon dioxide concentration ([CO 2 ]) have been studied extensively. However, long‐term effects of elevated [CO 2 ] (e[CO 2 ]) over multiple cropping generations have received little attention. Using open‐top chambers (OTCs), we set up ambient [CO 2 ] (CK) and two multigeneration e[CO 2 ] treatments during rice ( Oryza sativa L.) growing seasons in 2016–2019: a stepwise increase (SI) up to +160 μmol mol −1 in 2019 and a constant increase (CI) of +200 μmol mol −1 above CK over four generations. Beginning in 2017, grains harvested from the previous year in different [CO 2 ] treatments were used as seeds. Seedlings derived from CK OTCs in 2018 were transplanted into both SI and CI OTCs in 2019 to simulate single‐generation abrupt elevation of [CO 2 ]. We measured the diurnal changes in photosystem II (PSII) functionality of leaves in 2019. Single‐generation elevation of [CO 2 ] had no effects on PSII efficiency. However, a stepwise increase of [CO 2 ] over four generations significantly enhanced predawn maximum photochemical efficiency of PSII (F v /F m ), the efficiency that trapped exciton moves an electron beyond Q A − (ψ o ), and the quantum yield of electron transport (φE o ) in PSII at jointing stage. The constant increase of [CO 2 ] over four generations dramatically improved predawn F v /F m , ψ o , φE o , perform index, and reaction center at grain‐filling stage. Moreover, the multigeneration elevation of [CO 2 ] weakened the depression of F v /F m relative to single‐generation elevation at midday. All of these results indicated that e[CO 2 ] had transgenerational effects on PSII functionality.