Physiological responses of Agriophyllum squarrosum and Setaria viridis to drought and re-watering.

Drought resistance of psammophyte determines survival and growth, but their responses to drought are not well understood. We conducted a pot experiment to study how physiological characteristics respond to drought and rehydration. We found that watering to 60-65% of field capacity (the control) provided more water than was required by Agriophyllum squarrosum and its leaves became yellow and slightly wilted. 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. 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. During the late drought, the activities of three antioxidant enzymes in A. squarrosum increased to prevent membrane lipid peroxidation; for S. viridis, only peroxidase and superoxide dismutase activities increased. After rehydration, RWC of both species increased, but Fv/Fm of A. squarrosum and Fm of S. viridis did not recover under severe drought. Our research illustrated that A. squarrosum is better adapted to arid environment than S. viridis, but the high soil moisture content is not conducive to normal growth of A. squarrosum.