The effects of drought are intricate due to the different combinations of environmental characteristics and plant characteristics, including species differences 1, 16. Therefore, plant antioxidant enzyme defense function plays an important physiological role in plant stress resistance.

The accumulation of ROS in plants also activates a protective system of antioxidant enzymes, with increased activities of antioxidant enzymes such as catalase, superoxide dismutase (SOD) and peroxidase, which scavenge excess ROS to maintain a balance between an active oxygen metabolism and reducing the damage to cell membranes caused by ROS 14, 15.

At the same time, many studies have indicated that plants can produce high levels of reactive oxygen species (ROS)under adversity, which results in increased membrane permeability (due to peroxidation of membrane lipids), protein inactivation, and even plant death 1, 13.

viridis is consistent with the results 12. Studies have shown that plants osmoregulation can be carried out by accumulating osmotic regulator to maintain cell water balance, and our research about A. Thus, dryland ecosystems respond rapidly to precipitation changes 11. Water availability limits vegetation in arid ecosystems by affecting photosynthesis, net productivity, and plant survive, both in natural vegetation communities and after ecological restoration 3, 10. Many plants have evolved multiple mechanisms and strategies to adapt to water deficits through long-term natural selection and coevolution 8, 9. Drought causes water loss from plant cells, which leads to major changes in plant morphology, physiology, and biochemistry, and limits the growth range and living space of many species 6, 7. With the global climate changing and the environment deteriorating, water shortages have become increasingly serious, causing a more intense situation on drought stress 5. To understand plant survival under these conditions, it is necessary to comprehend the mechanisms that underlie plant physiological responses to drought and re-watering. Hence, plants are subjected to repeated cycles of drought and rehydration throughout their life cycle by this highly variable climate 4. Water in these areas is unevenly distributed both temporally and spatially, and often does not satisfy plant needs 2, 3. The worldвЂ™s arid and semi-arid regions account for about one-third of the land area, versus nearly half of terrestrial land in China 1. viridis, but the high soil moisture content is not conducive to normal growth of A. squarrosum is better adapted to arid environment than S. viridis did not recover under severe drought. After rehydration, RWC of both species increased, but Fv/ Fm of A. viridis, only peroxidase and superoxide dismutase activities increased. squarrosum increased to prevent membrane lipid peroxidation for S. During the late drought, the activities of three antioxidant enzymes in A. With increasing drought duration and intensity, the relative water content (RWC), chlorophyll content, Fm, and the quantum efficiency of photosystem II ( Fv/ Fm) of Setaria viridis decreased, but malondialdehyde and membrane permeability increased. The total chlorophyll content and Fm (maximum fluorescence after dark adaptation) in control were lower than in the drought treatment, and both decreased after rehydration. We found that watering to 60вЂ“65% of field capacity (the control) provided more water than was required by Agriophyllum squarrosum and its leaves became yellow and slightly wilted. We conducted a pot experiment to study how physiological characteristics respond to drought and rehydration. Drought resistance of psammophyte determines survival and growth, but their responses to drought are not well understood.

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