Growth and Physiological Responses of Magnoliaceae to NaCl Stress

The growth and physiological characteristics of four Magnoliaceae plants (<i>Yulania biondii</i>, <i>Yulania denudata</i>, and two varieties of <i>Magnolia wufengensis</i> (Jiaohong 1 and Jiaohong 2)) were investigated. Four Magnoliaceae plants were subjected to various concentrations of NaCl for 60 days: 0 mM, 60 mM, 120 mM, 180 mM, and 240 mM. The leaf water content (LWC), relative growth rate of plant height and stem diameter, photosynthetic pigments, and photosynthetic rate (<i>P_n</i>) decreased during the NaCl treatments, indicating slowed growth and photosynthesis. Malondialdehyde (MDA), Na⁺, superoxide dismutase (SOD) activity, peroxidase (POD) activity, ascorbic acid (AsA) content, and soluble sugar content all increased while K⁺ decreased. Ascorbate peroxidase (APX) activity, glutathione (GSH), soluble protein, and proline first increased after decreasing with increasing NaCl concentration. Principal component 1 (PC1) had larger loading values for growth and photosynthesis indices, while principal component 2 (PC2) exhibited larger loading values for antioxidant substances and osmotic adjustment substances; the correlation analysis showed that PC1 and PC2 had negative correlations. The four Magnoliaceae plants exhibited largely variable growth and physiological activities in response to NaCl. <i>Yulania denudata</i> exhibited greater reductions in growth and photosynthesis and greater decreases in antioxidant enzyme activities and osmotic adjustment substances, which indicated poor tolerance to salt stress. Among the four Magnoliaceae plants, Jiaohong 1 exhibited the greatest salt tolerance, followed by Jiaohong 2, <i>Yulania biondii</i>, and <i>Yulania denudata</i>.