中华蚊母树种群在三峡水库水位涨落下的水淹耐受性与生长适应机制

The water-level-fluctuation zone of the Three Gorges Reservoir was assumed to be completely formed in 2009 and the water level would range from 145 m in flood season (summer) to 175 m during non-flood season (winter)． This hydrologic regime is the opposite of the Yangtze River's natural regime before the Three Gorges Dam construction when the peak flows occurred in summer and low flows occurred in winter. The reversal of flooding time and prolonged flooding duration will dramatically alter environmental conditions in the riparian zone. The fragility of the water-level-fluctuation zone has been widely recognized by Chinese scientific community and governments．It is common view that vegetation should be given a priority for ecological restoration in the water-level fluctuation zone．Therefore, screening and selection of promising plant species that have the tolerance to flooding and draught is urgent for vegetation restoration and reconstruction in the water-level-fluctuation zone of the Three Gorges Reservoir. While the most experimental screening of submergence-tolerant species has been conducted on annual and perennial herbaceous plants in the water-level-fluctuation zone, relatively few studies were focused on screening of native submergence-tolerant shrubs or shrublets, which would be of great significance for biodiversity conservation and to maintain a functioning riparian area with less susceptibility to encroachment of non-native species. Distylium chinense, the genus Distylium of the Hamamelidacea, is an evergreen perennial shrub between 0.8 and 1.2m in height, native to the riparian areas and wetlands and a dominant species in the middle and upper areas of the water-level-fluctuation zone of the Three Gorges Reservoir Region of the Yangtze River and its branches. In the present study, seed germination, and seedling recruitment, morphology and photosynthesis of seedlings of different geographic D. chinense populations after submergence stress and their recovery growth after soil drainagein different elevation sections (160-175m) of the water-level-fluctuation zone of the Three Gorges Reservoir were investigated, variation of population genetic structure was analyzed in the molecular level and the relationship among their submerged-tolerance and their genetic structure variation, the ecological environment they live in was discussed, namely, submergence tolerance and growth acclimation mechanism of different geographic D.chinense populations were investigated in morphologic, photosynthetic and molecular level. After that, the submergence tolerance and recovery growth status of seeds and seedlings of different geographic D.chinense populations were comprehensively evaluated by using membership function method of fuzzy mathematics in order to screen and select promising D.chinense population, which would provide scientific data for vegetation restoration and reconstruction in the water-level-fluctuation zone of the Three Gorges Reservoir.

开展消落带植被恢复和重建是三峡水库生态环境治理的一项重要举措，筛选适生于消落带的植物材料是当前亟待解决的问题。在消落区的植被构建中，大多为草本植物，因此选用耐淹的本土灌木尤为迫切。中华蚊母树(Distylium chinense)是三峡水库消落区中上部的主要灌木之一。本项目以不同地理来源的中华蚊母树种群为研究对象，研究在三峡水库消落区不同高程（160-175m）水位涨落下种群种子萌发与幼苗定居、幼龄种群水淹后恢复生长过程中形态生长的适应性和光合特性；并从分子水平分析种群遗传结构与遗传分化，探索水淹胁迫下种群的水淹耐受性与遗传结构的变异和所处生态环境条件之间的联系，即从形态、光合和种群遗传结构综合探索中华蚊母树种群的水淹耐受性及生长适应机制。同时采用模糊数学中隶属函数法综合评价不同中华蚊母树种群的水淹耐受性差异，筛选出适宜的中华蚊母树种群，为三峡水库消落区的植被恢复与重建提供基础科学数据。

本项目通过在三峡水库消落区的野外定位研究和室内水淹模拟实验与室内分析相结合的方式，运用植物生态学和分子标记技术相结合的方法，从形态、光合和种群遗传结构综合探索了三峡库区不同地理来源的中华蚊母树种群的水淹耐受性及生长适应机制，揭示了中华蚊母种群在不同水文节律的异质生境下的生态适应性的主要驱动因子。主要研究结果如下：.1）通过在三峡库区消落区野外水淹实验和室内控制的水淹实验研究，结果表明中华蚊母树在三峡水库173-175m消落区可以存活，表现较高的存活率，水淹后恢复生长较快，主要表现根、茎、叶碳水化合物（淀粉和可溶性糖）的恢复模式与嫩枝、主茎长、新叶、光合速率的恢复及生物量的积累是一致的。本研究首次提供实验证据证明中华蚊母树将更多的碳水化合物分配到根和茎以提高其对长期完全水淹的耐受性。碳水化合物的储备，特别是在根和茎，是一个解释低生长-高存活-快速恢复生长之间权衡的一个重要的功能特性，这可能就是中华蚊母树对长期水淹的一种有效适应策略。.2）野外调查中华蚊母树种群在自然消落带区、反季节消落带区及无消落带生长区等3种异质生境下9个不同种群叶片主要功能性状的表型可塑性及其与环境因子的相互关系。结果表明，异质生境中种群叶片较大的表型可塑性和生长一致性表明了尽管中华蚊母树较宽幅的适应性但仍然表现生长的一致性。同时采典范对应分析(CCA) 探讨了中华蚊母树叶片性状与环境因子之间的关系，结果显示海拔高度、土壤pH值、速效钾及全氮是中华蚊母树适应水淹不利异质生境下的主要驱动因子，通过这些环境因子的驱动改变叶面积、叶干重及比叶面积等关键功能性状使中华蚊母树能在不同水文节律生境中表现出最佳的适合度，使中华蚊母树能够适应三峡水库长期水淹的不利生境。.3）ISSR和SRAP分子标记分析表明，遗传多样性丰富的种群水淹耐受能力越强，并采用了隶属函数法综合评价了种群的水淹耐受性表明以古龙溪、竹子溪北岸和南岸以及古龙溪种群的水淹耐受性较其它种群好。对群落、物种及环境因子进行了PCA和CCA分析表明，土壤水分含量、全磷、速效钾及有机质是影响群落物种组成和分布的主要驱动因子。可见中华蚊母树可以适应30-120d的完全水淹，表现较高存活率，水淹节结束后表现快速的恢复生长能力，是一种水淹耐受能力较强的小灌木树种，适合在三峡水库消落区173-175m处生长。在三峡水库的恢复与重建中可考虑为本土首选小灌木树种。