In conclusion, we showed that the combined treatment improved photosynthesis at 81.6 lM LaCl3 and pH 4.5 of acid rain, whereas all other levels of combined treatment inhibited photosynthesis in rice during the whole growth stages. Combined treatments past the threshold of concentrations of 81.6 lM LaCl3 and acid rain at pH 3.5 began to have toxic effects on photosynthesis. Furthermore, an important observation in this study is that throughout the whole growth stage, the booting stage in rice was the most sensitive stages to the combined treatment of LaCl3 and acid rain. Our study therefore provides novel insights into the combined effects of REEs and acid rain on plants, and might also serve as important documentation to evaluate the biological safety of REE pollution in agricultural areas.