[Effects of drying and re-watering on the photosynthesis and active oxygen metabolism of Periploca sepium seedlings].

Taking two-year-old Periploca sepium seedlings as test materials, an experiment with controlled soil water contents was conducted to study the effects of repeated drying and re-watering on the leaf photosynthetic characteristics and the lipid peroxidation and antioxidant system in young leaves, mature leaves, old leaves, new stems, and fine roots. The seedlings were subjected to three cycles of drying and re-watering, with regular irrigation to maintain the soil water content at around 80% of field capacity as the control (CK). Under drying, the leaf relative water content (RWC) and net photosynthesis rate (Pn) decreased significantly, while the leaf photosynthetic pigments content increased. When the seedlings were re-watered, their leaf RWC recovered to the CK level, showing a strong repair capacity after drying. Both the leaf chlorophyll content and the Pn after repeated drying and re-watering presented a higher level than those of the CK, indicating a compensatory effect appeared and an appropriate drought stress being able to induce the adaptability of P. sepium to drought stress. Stomatal closure was the main factor limiting P. sepium photosynthesis under drought stress, while non-stomatal limitation only worked at noon. Under drying, the superoxide anion radical (O2-*) production rate in young leaves, new stems, and fine roots increased while the malondialdehyde (MDA) contents decreased, suggesting that these young tissues were not suffered from the oxidative stress. The activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) in different organs had different variation trends, with those in fine roots changed actively, suggesting the important role of fine roots in the acclimation of P. sepium to drought environment. It was the cooperation and coordination among plant organs that made P. sepium more adaptive to the repeated drying and wetting conditions in drought-prone regions.