Effects of Silicon on the Growth, Photosynthesis and Chloroplast Ultrastructure of Oryza sativa L. Seedlings under Acid Rain Stress

Silicon (Si) is a beneficial element for plants and can increase plant resistance. In the present work, a hydroponic experiment was carried out to study the effects of Si on the growth and photosynthesis of rice (Oryza sativa L.) seedlings under simulated acid rain (SAR) stress. The growth, photosynthesis and chloroplast ultrastructure of rice seedlings treated with combined or single weak SAR (pH 4.0) and/or Si (1, 2 or 4 mM) were improved. Spraying with moderate or severe SAR (pH 3.0 or 2.0) significantly inhibited the growth and photosynthesis and severely damaged the chloroplast ultrastructure of rice seedlings. The incorporation of exogenous Si increased the growth and photosynthesis and improved the chloroplast ultrastructure of rice seedlings treated with moderate or severe SAR (pH 3.0 or 2.0). The 2.0 mM Si treatment had more significant promoting or alleviating effects than the 1 and 4 mM Si treatments. The stomatal conductance (G(s)), chlorophyll content, maximum quantum efficiency of PSII photochemistry (F-v/F-m), actual photochemical quantum efficiency of PSII photochemistry (Y) and chloroplast ultrastructure were improved with the addition of Si to the SAR treatment, which indicated that the positive effect of Si on photosynthesis was partly associated with stomatal and non-stomatal factors. Thus, Si fertilization improves rice resistance to acid rain.