种子遗传质量是否是限制水青树种群更新的根本原因？-以美姑龙窝水青树种群为例

Tetracentron sinense Oliv. is a relic plant with old origin, and has been listed as the national second-grade protected plant species in China. The species has important ecological and environmental fuctions, and is also highly valuable for scientific research and application in medicine, timeber and ornament. The existed researches showed that there are a large number of seeds per tree, but the seedling are rare during natural regeneration of T. sinense population, which resulted in difficult regeneration of the population. So far, the occurring course and influencing factors are still not clear. Therefore, knowledge of the characteristic of natural regeneration of T. sinense and its influencing factors is necessary for providing valuable information to suggest appropriate conservation measures and for the sustainable utilization of T. sinense. Based on the precious studies and necessary conditions of successful natural regeneration of plant, the key links during life history of the species such as seed production, seed dispersal, seedling survival and sapling establish, will be studied in this project with the ecological methods of population, seed and seedling. Through the project, the occurring course and influencing factors of natural regeneration of T. sinense population will be analyzed, and whether the seed genetic quality is the root cause influencing natural regeneration of T. sinense population will also be tested, which can provide the theoretical foundation for the recovery and enlargement of population. In addition, the results from the project can also provide scientific basis for the germplasm resources protection and sustainable utilization of T. sinense, and the research methods in the project can provide the reference for the conservation biological research of other endangered plants.

水青树是地球上起源古老的孑遗植物，属国家二级保护植物，具有重要的生态、药用、材用、观赏和科学研究价值。现有研究表明，水青树种群中单株结实量较大，但实生苗匮乏，种群呈现幼龄个体少、成年个体较多的特点，自然更新困难，其发生过程和影响因素至今尚不明确。科学认识水青树自然更新机制，进行相应的种群保护与扩大，实现水青树天然资源可持续利用已十分必要。本项目拟从植物自然更新的必要条件出发，利用时空模型研究模式，结合种群生态学、种子和幼苗生态学研究方法，对水青树种群种子的生产、扩散、幼苗定居和幼树建成等生活史关键环节进行究，分析水青树种群更新限制的发生过程及其影响因素，揭示种子遗传质量是否是限制水青树种群更新的根本原因，为制定合理的保育措施促进水青树野生种群恢复和扩大提供理论基础，为水青树种质资源的有效保护与可持续利用提供科学依据，还可为其它濒危植物的保护生物学研究提供参考。

水青树为水青树科唯一幸存的高大落叶乔木，野生种群呈现幼苗个体较少、中老龄个体较多的特点，自然更新困难，被列为国家二级重点保护植物。本项目根据时空模型研究模式，利用种群生态学、种子及幼苗生态学研究方法，对水青树生活史过程的关键环节进行研究，分析其种群更新限制的发生过程及影响因素，验证种子遗传质量是否是限制水青树种群更新的根本原因，为水青树种质资源的有效保护与管理提供科学依据。. 研究发现：（1）水青树种子处于吸胀期时，一定范围内低温冷冻对其种子的萌发并无抑制作用。（2）光照太强或太弱均不利于水青树种子的萌发；（3）出苗后的第2个月是水青树幼苗生存的瓶颈期；水青树在幼苗生长初期具有适度耐阴的特性；自然生境中暴雨的冲刷可能是影响其生存的重要因素。（4）中度光照下、适度覆盖枯落物和灌草丛有利于水青树幼苗的生长。（5）水青树种子无法散播到适宜于其萌发和幼苗生长、存活的环境，可能是限制水青树种群更新的主要因素之一。（6）为适应恶劣的环境条件和过小的种群密度，水青树形成了自交的繁殖策略；种子遗传质量显著影响水青树种子和幼苗的质量，异株异花授粉处理的种子和幼苗质量均明显优于自然授粉处理。（7）不同遗传质量的水青树幼苗存活的瓶颈期均出现在出苗后的前2个月；在不同生境条件下，异株异花授粉处理的水青树种子和幼苗的适合度整体上明显优于自花和自然授粉处理。. 结果表明：（1）吸胀期低温冷冻不是限制水青树种群更新的主要因素；水青树野生种群存在典型的传播限制；种子遗传质量的确是限制水青树种群更新的重要因素。（2）在种子萌发阶段，增加林窗或林缘环境，去除覆盖种子的枯落物及灌草层，可促进种子的萌发；在幼苗前期应为幼苗创造适度遮阴和避雨的条件，确保幼苗的存活和生长。此外，应通过从较近种群引种，以增强种群间的基因交流和促进种群的恢复与扩大，提高异交的几率，以提高其种子和幼苗的适合度，促进种群的自然更新。

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