Response And Adaptation Mechanism Of Seedlings Of Tsuga Longibracteata To Extreme Temperature And Extrinsic Calcium

Tsuga longibracteata is considered as one of the excellent tree speices for restoration in southern China. To explore the ecophysiological response of its seedling to extreme temperatures, the chlorophyll in leaves, lipid peroxidation activities of antioxidant enzymes, osmoregulation, water contents, as well as the contents of calcium in leaves and roots of Tsuga longibracteata seedling were studied under low and high temperature stresses with extrinsic calcium. The results showed that:(1) The leaves of Tsuga longibracteata seedlings could grow in good contition and keep certain photosynthetic characteristics under the low temperature stress (LTS). As temperature decreasing, contents of photosynthetic pigment, soluble sugar, proline (Pro), calcium and malondialdehyde (MDA) increased, while activities of the antioxidants superoxide dismutase (SOD) decreased, and activities of peroxidase (POD) enhanced.(2) As temperature decreasing, the content of Pro in the roots of Tsuga longibracteata seedlings increased, MDA and calcium increased at first and then declined below -4℃.(3) Although the regulation and recovery of leaves and roots under LTS are different, still their effects in total help Tsuga longibracteata to stand a rather cold stress, its long-term evolution make it an excellent tree species to adapt the extreme subtropical climate.(4) The content of photosynthetic pigment, water content and Ca2 + concentration in leaf was increased at first and then decreased under high temperature stress (HTS). Also, higher water content can improve the metabolism of plant tissue.(5) Both SOD and POD activity declined with temperature increasing in root, but the content of MDA, soluble sugar and Pro increased. From 30℃to 35℃, MDA content in leaf increased, due to the decreasing of both SOD and POD activity. Whereas, SOD and POD activity increased under extreme the temperature 50℃, with soluble sugar and Pro also increased synchronously, which can improve membrane stability.(6) The results indicated that Tsuga longibracteata seedlings can stand with HTS, and the most suitable growth temperature is ranged from 30℃to 35℃.(7) Extrinsic calcium plays an important role of increasing the ability of Tsuga longibracteata seedlings to endure severe temperature. Extrinsic calcium could enrich Chla, Chlb, Chl and Car contents, while enhance sugar metabolism and SOD activity. The process of photosynthesis in Tsuga longibracteata seedlings rich its top under the 0.4mg·g-1 extrinsic calcium treatment.