Objective  The main purpose of this study was to explore how Robinia pseudoacacia coped with drought and rehydration caused by climate change, and to understand the changes of water physiology, non-structural carbon balanced allocation strategy and physiological and biochemical response mechanism during drought and rehydration. It helps to reveal the physiological mechanism of Robinia pseudoacacia forest decline and death under the background of overall climate change. Theoretical reference for cultivation irrigation of Robinia pseudoacacia forest was provided.

  Method  In this study, the experimental method of natural drought was used, and the normal water supply was set and the water supply was stopped. Then, the physiological indexes of two years old Robinia pseudoacacia seedlings were measured, such as water status, pressure-volume curve parameters, non-structural carbon and antioxidant enzyme activities, and the effects of different treatments and period of drought on physiological parameters of Robinia pseudoacacia seedlings were compared.

  Result  In the light drought period, the accumulation of starch and the ability of maintaining turgor pressure in cells of Robinia pseudoacacia leaves increased, and the osmotic regulation and antioxidant defense mechanism of roots and leaves were also started. During moderate drought period, the process of starch conversion to soluble sugar and Pro content increased significantly to improve osmotic regulation to cope with drought stress. At the same time, the activities of APX, SOD and POD reached peak values, and the osmotic regulation and antioxidant defense mechanism of root were fully activated. When Robinia pseudoacacia was in a severe drought, the content of starch and NSC in roots increased, the function of NSC gradually changed from the osmotic regulation of soluble sugar to the accumulation of starch. After rehydration, root and stem storage NSC decreased significantly.

  Conclusion  The growth of Robinia pseudoacacia seedlings is significantly inhibited by drought stress, and its water transport, carbon metabolism and other physiological and biochemical reactions are significantly affected. When drought stress exceeds moderate drought, the physiological adaptability of Robinia pseudoacacia seedlings decreases. As drought stress intensifies, a net loss of carbohydrates may occur. During severe drought, more NSC seedlings will be distributed from leaves to roots, and NSC will gradually be used for osmotic regulation to storage, and may be used for restoration and reconstruction of hydraulic conduction after rehydration.