Dual Role of Acid Rain and Pyricularia oryzae on Growth, Photosynthesis and Chloroplast Ultrastructure in Rice Seedlings

Rice is widely planted and serves as staple food in the world, but it is often exposed to acid rain and rice blast (Pyricularia oryzae). In this work, we analyzed the effects of co-exposure to simulated acid rain (SAR) and P. oryzae on the photosynthetic growth of rice seedlings. We found that the growth, photosynthesis, and chloroplast ultrastructure of rice seedlings were damaged under single treatments of P. oryzae and strong acid rain (pH 2.0) but increased under medium acidity acid rain (pH 4.0). Similarly, when plants were exposed to both P. oryzae and acid rain, pH 4.0 mitigated the changes of growth, photosynthetic characteristics, and chloroplast ultrastructure induced by P. oryzae, but pH 2.0 aggravated these changes. In addition, we found that significant differences in chlorophyll content (chlorophyll a and chlorophyll b) correlated with transpiration rate (Tr) under the combined stress of acid rain and P. oryzae at pH 4.0 and pH 2.0. Medium-acidity acid rain alleviated the harm caused by P. oryzae on rice growth by enhancing synergistic regulatory mechanisms of photosynthetic traits to increase plant resistance tolerance. The effect of P. oryzae on photosynthetic traits of rice was regulated by acidity of acid rain.