Effects of exogenous 2, 4-epibrassinolide on the growth and photosynthesis of alfalfa under high temperature and low light stress in summer

doi:10.11686/cyxb2019511

Abstract

Abstract: This study investigated the regulatory effects of exogenous 2, 4-epibrassinolide (EBR) on the growth and photosynthesis of alfalfa under high temperature and low light stress in summer. A simulated shade experiment with green shade mesh was conducted by setting up three light environments [full sunlight (L₀), 46.30% sunlight (L₁), and 28.63% sunlight] and four EBR concentrations [distilled water (CK), 0.01, 0.1, and 1 mg·L^-1]. The effects of EBR on the morphology, growth, photosynthetic pigment content, photosynthetic parameters and photosynthetic light-response curve were assessed. Results showed that the photosynthetically active radiation (PAR), red to far-red (R∶FR) ratio and percentages of the red and violet bands in PAR on the alfalfa canopy significantly decreased and that the percentage of the green band significantly increased with increasing shade in summer. Compared with CK, the leaf area, leaf mass rate, internode length, acropetal angles between leaf and mainstem, chlorophyll a and b contents, and intercellular CO₂ concentration significantly increased, and temperature of the leaf thermocouple (T_leaf) and carotenoid content significantly decreased under shaded conditions. Compared with L₀, the net photosynthetic rate and maximum net photosynthetic rate did not show distinct changes with 1 mg·L^-1 EBR treatment under L₁ in summer. The results of Pearson correlation analysis showed that PAR, R∶FR, and the percentage of the violet band on the alfalfa canopy had significant positive correlations with light intensity under shaded conditions. The root mass rate had a distinctly negative correlation, and the node number of the mainstem had no significant correlation with light intensity under EBR or shade treatments. The above results indicate that exogenous EBR can regulate the plant structure, decrease T_leaf, promote the synthesis of photosynthetic pigments, and improve the photosynthetic efficiency, and in this way alleviate high temperature and low light stress in alfalfa. Among the rates tested, 1 mg·L^-1of EBR was the optimal concentration to improve the growth of alfalfa under slight shading (L₁) during the summer period.

Key words: alfalfa, summer, shading, photosynthetic pigment, photosynthetic light-response curve

QIN Feng-fei, LI Zhi-hua, LIU Xin-bao, QU Hui, PINGCUO Zhuo-ma, LUOSONG Qun-cuo, SU Meng-han. Effects of exogenous 2, 4-epibrassinolide on the growth and photosynthesis of alfalfa under high temperature and low light stress in summer[J]. Acta Prataculturae Sinica, 2020, 29(9): 146-160.

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