Study On Mechanism Of Flooding Tolerance Of Taxodium ’Zhongshanshan’

In order to research the flooding tolerance of Taxodium ’zhongshanshan’, In March 2014, we investigated the preserving rate and growth situation of Taxodium ’zhongshanshan’. The results showed: average preserving rate of Taxodium ’zhongshanshan’ in 163-174m elevation was 98.1%. Its average height of trees exceeded 3.5 meters, average DBH (diameter at breast height) exceeded 4 centimeter, the depth of water had no significant effect on the height of trees, but had significant effect on DBH. Pole-strength flooding tolerance of Taxodium ’zhongshanshan’ laid a solid foundation for improving the Yangtze River three gorges reservoir area by biological measures.In order to research the mechanism of flooding tolerance of Taxodium ’zhongshanshan 118’,24 1-year Taxodium’zhongshansha 118’[(Taxodium. distichum×Taxodium. mucronatum) ×Taxodium. mucronatum] seedlings were randomly and equally divided into four groups and each group experienced one of four different levels of waterlogging (i.e., no waterlogging, waterlogging, partial submergence, deep submerged) from August 8 to November 8,2014 and December 11 to April 13,2015.After the flooding treatments, The mechanism of the tolerance of Taxodium’zhongshansha 118’to long-term waterlogging was investigated through the measurements and analysis of the changes in the contents of anaerobic respiration enzymes (e.g., lactic dehydrogenase (LDH), ethanol dehydrogenase (ADH) and pyruvate decarboxylase (PDC)), root starch and soluble sugar in the’Zhongshansa118’ seedling, the light/CO2 response curves of net photosynthetic rate (PN) and activities of antioxidant enzymes [i.e., Superoxide Dismutase (SOD), Catalase (CAT) and Peroxidase (POD)],non-enzymatic antioxidant(proline, ascorbic acid and glutathione) in the roots and leaves. The biomass and activity of the seedling roots were also measured and analyzed.1.Net photosynthetic rate (PN) decreased significantly due to partial and deep submergence, but the PN of waterlogging treatment are maximum, maximum rate of carboxylation (Vcmax), maximum potential rate of electron transport (Jmax) and triose phosphate utilization rate (TPU) are similar to PN, which indicates waterlogging promote the photosynthetic capacity of Taxodium hybrid (Zhongshansha 118) leaves. There is no obvious significance in dark respiratory rate in leaves indicating carbon loss is not decreased due to flooding treatments.2. Activities of antioxidant enzymes in roots and leaves of Taxodium hybrid (Zhongshansha 118) are increasing with degrees of flooding treatments in growing season. The Activities of CAT and POD in non-growing season are similar to growing season, but activity of SOD is opposite. After 93 days flooding treatments during growing season, activities of antioxidant enzymes [i.e., Superoxide Dismutase (SOD), Catalase (CAT) and Peroxidase (POD)] in four groups in leaves are higher than in roots, the Activities of CAT and POD in non-growing season are similar to growing season, but activity of SOD is opposite, leaves are more sensitive to flooding. Oxidative stress is happened in Taxodium hybrid (Zhongshansha 118) both in growing season and non-growing season waterlogging, however the species and number of ROS are different between growing season and non-growing season waterlogging. Taxodium hybrid (Zhongshansha 118) suffering waterlogging in growing season are more complicated than non-growing season.3.The contents of the anaerobic respiration enzymes in the seedling roots and leaves are increasing with the levels of severity of waterlogging. The contents of the anaerobic respiration enzymes in the seedling roots in growing season are higher than it in non-growing season, but leaves have opposite trend, which indicated the roots and leaves adapt to long-term waterlogging by reinforceing anaerobic respiration, activities of ADH in roots and leaves were higher than LDH, so roots and leaves used alcoholic fermentation mainly.4.The starch and soluble sugar in roots and leaves had similar trend with anaerobic respiration enzymes, but roots starch were higher than leaves while soluble sugar were lower than roots, the higher content of starch were the important reason of strong submergence tolerance, and we consider the strategy to fit into long-term waterlogging is patience type.5. while it have aerial root and basal part of stem expand, the outer wall of the root are lignified to protect the roots from waterlogging, Taxodium’zhongshansha 118’also have the morphological property to adapt to long-term waterlogging.Taxodium hybrid (Zhongshansha 118) show the strong tolerance to flooding, it can be considered to act as the plant of wetland ecology repair to carry on planting experiment.