Improvement of Cerium on Photosynthesis of Maize Seedlings Under a Combination of Potassium Deficiency and Salt Stress

Added Ce³⁺ can partly substitute for Ca²⁺ or Mg²⁺ and improve photosynthesis under the deficiency of these elements, but very few studies focused on photosynthetic improvement in maize seedlings caused by K⁺ deficiency, salt stress, especially a combination of K⁺ deficiency and salt stress. In the present study, the effects of Ce³⁺ on the photosynthesis of maize seedlings under the three different stresses were investigated. The results showed that added Ce³⁺ under various stresses increased the ratios of free water/bound water and of K⁺/Na⁺, the pigment contents, the values of Fv/Fm, Y(II), ETR(II), Y(NPQ), Qp, qL, NPQ, and qN of photosystem II (PSII), the values of Y(I) and ETR(I) of photosystem I (PSI) and the expression levels of LhcII cab1 and rbcL, and decreased the values of Y(NO) and Y(NA). This implied that added Ce³⁺ depressed ion toxicity, photodamage of PSII, and acceptor side constraints of PSI, and enhanced adjustable energy dissipation, the responses of photochemistry, and carbon assimilation caused by K⁺ deficiency, salt stress, and the combination of K⁺ deficiency and salt stress. However, Ce³⁺ mitigation of photosynthetic inhibition in maize seedlings caused by the combined stresses was greater than that of salt stress, and Ce³⁺ mitigation under salt stress was greater than that under K⁺ deficiency. In addition, the results also showed that Ce³⁺ cannot improve photosynthesis and growth of maize seedlings under K⁺ deficiency by substituting for K⁺.