Quercus dentata responds to Na 2 CO 3 stress with salt crystal deposits: ultrastructure, and physiological–biochemical parameters of leaves

Key message Our study elucidated that Q. dentata responds to Na 2 CO 3 stress by excreting salt on the blade, accumulating osmotic protectants, and changing the cell ultrastructure and physiological-biochemical parameters of leaves. Abstract Quercus dentata Thunb is an important constructive species in the forest communities of the mountainous areas of northern China with high ecological and landscape value. However, soil salinization prevents the use of Q. dentata in the North China Plain. Therefore, it is necessary to explore how Q. dentata responds to saline-alkaline stress. Here, Q. dentata seedlings were exposed to different concentrations of an alkaline salt (Na 2 CO 3 ) to determine the effects on leaf mesophyll cell ultrastructure and physiological-biochemical parameters. We first discovered crystallized deposits on the pressure side of Q. dentata leaf blades after the 100 mM Na 2 CO 3 treatment. Scanning electron microscopy and energy-dispersive X-ray analysis revealed that the main component of the crystal deposits was sodium ions. However, no salt glands or bladders were detected in Q. dentata leaves. Moreover, the ultrastructure of the mesophyll cells changed as stress duration increased, and the number and size of the chloroplasts were limited by partial disintegration. The results also show that Na 2 CO 3 -stressed Q. dentata plants displayed increased soluble sugar and proline contents. Additionally, the low-concentration Na 2 CO 3 stress slightly enhanced the activity of antioxidant enzymes, such as catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD). In summary, the results show that the cell structure of Q. dentata leaves was damaged by Na 2 CO 3 stress. However, accumulating osmoprotectants and the excretion of salt onto the leaf blades enhanced saline-alkaline stress tolerance.