Calcium amendment for improved germination, plant growth, and leaf photosynthetic electron transport in oat (Avena sativa) under NaCl stress

Calcium (Ca(2+)) is an essential nutrient element for plants as it stabilizes the membrane system structure and controls enzyme activity. To investigate the effects of Ca(2+) on plant growth and leaf photosynthetic electron transport in oat (Avena sativa) under NaCl stress, oat seeds and plants were cultivated in nutrient solutions with single NaCl treatment and NaCl treatment with CaCl(2) amendment. By measuring the seed germination rate, plant growth, Na(+) and Cl(-) accumulation in leaves, ion leakage in seedlings and leaves, prompt chlorophyll a fluorescence (PF) transient (OJIP), delayed chlorophyll a fluorescence (DF), and modulated 820 nm reflection (MR) values of the leaves at different growth phases, we observed that Ca(2+) alleviated the inhibition of germination and plant growth and decreased Na(+) and Cl(-) accumulation and ion leakage in the leaves under NaCl stress. NaCl stress changed the curves of the OJIP transient, induced PF intensity at P-step (F(P)) decrease and PF intensity at J-step (F(J)) increase, resulted in obvious K and L bands, and altered the performance index of absorption (PI(ABS)), the absorption of antenna chlorophyll (ABS/RC), electron movement efficiency (ETo/TRo), and potential maximum photosynthetic capacity (F(V)/F(M)) values. With the time extension of NaCl stress, I(1) and I(2) in the DF curve showed a decreasing trend, the lowest values of MR/MR(O) curve increased, and the highest points of the MR/MR(O) curve decreased. Compared with NaCl treatment, the extent of change induced by NaCl in the values of OJIP, DF and MR was reduced in the NaCl treatment with CaCl(2) amendment. These results revealed that Ca(2+) might improve the photosynthetic efficiency and the growth of salt-stressed plants by maintaining the integrity of oxygen-evolving complexes and electron transporters on the side of the PSI receptor and enhancing the relationship between the functional units of the photosynthetic electron transport chain. The findings from this study could be used for improving crop productivity in saline alkali lands.