Physiological response and stress tolerance mechanisms of Caragana korshinskii and Calligonum mongolicum suffering from taproot exposure

Wind erosion is the dominant factor of root exposure of sand-fixing plants.Eight years old plants of Caragana korshinskii and Calligonum mongolicum from Baijitan Nature Reserve of Ningxia were used as the experimental materials in this study. The taproots were exposed by three depths of 10 cm, 20 cm, and 30 cm, and their physiological processes and adaptation mechanisms were analyzed. The results showed that:（1） there was not any significant difference between the physiological parameters of Caragana korshinskii and those of the control within 21 days after the taproot was exposed by 10 cm. Caragana korshinskii showed significant differences in malondialdehyde content, Pro content, chlorophyll content, Chl（a/b）, and catalase on the 7 th day with the taproot being exposed by 30 cm compared to the control. These physiological parameters returned to the control level on the 21 st day. Both soluble sugar and superoxide dismutase values were not significantly different compared to the control from the beginning to the end. Therefore, 10 cm exposure of the taproot did not cause stress to Caragana korshinskii. Within seven days after the exposure by a depth of 30 cm, H2O2 was removed by activating an osmotic adjustment system mainly driven by free proline and enhancing CAT activity, so that the plant gradually returned to a physiologically stable state.（2） Calligonum mongolicum regulated the physiological homeostasis by an accumulation of soluble sugars and an increase of Chl（a/b） on the 7 th day after the taproot being exposed by 10 cm. The SOD, CAT, and chlorophyll contents were significantly lower than those of the control（P