Supplementary calcium can help enhance photochemical activity in peanuts ( Arachis hypogaea ) leaves under low night temperature stress

Exogenous calcium is able to maintain photosynthesis level under low night temperature (LNT) stress. Nevertheless, the mechanism for supplementary calcium to mitigate photosynthesis barriers under LNT has not been as clear as expected so far. This study mainly covered the response rules to Ca 2+ and Ca 2+ inhibitors for Photosystem II (PSII) photoinhibition, photochemical activity and allocation of absorbed light in leaves of peanut seedlings under low night temperature stress and during their recovery process. As the results indicated, low night temperature stress boosted excitation energy at PSII reaction centers of peanut leaves, and inhibited electron transfer, leading to imbalanced excitation energy distribution with lower photochemical efficiency between these two photosystems. The ratio of antenna heat dissipation increased, while the ratio assigned to photochemical reaction reduced in the process of light absorption, so photosynthetic efficiency declined. Foliar spray of exogenous calcium ameliorates the imbalanced excitation energy between Photosystem II(PSII) and Photosystem I (PSI), increasing electron transfer rate (ETR) and efficiency of light energy conversion at PSII reaction centers (Fv/Fm). More light energy is used for photosynthesis, thus promoting the growth of peanut seedlings. Supplementary calcium available helped to adjust PSII activity via increasing electron transfer rate, more excitation energy was transported to PSI, and the damage of PSII reaction center caused by excess excitation energy reduced. The increase of active reaction centers has enhanced the utilization efficiency of light energy.