短枝木麻黄花粉散布对生殖成功和子代适应性的影响

Pollen is the main carrier of gene flow in plant. Pollen dispersal distances and patterns affect not only genetic structures and diversities of plant population, but also reproductive success and progeny fitness of plant itself. According to published references, studies on pollen dispersal were mainly focused on naturally distributed plant under population scale, but effects of pollen dispersal of introduced tree species on reproductive success and progeny fitness under individual level have not been well documented. In this study, seeds from a female tree and twig samples from all potential pollen donors will be collected from a seedling plantation of Casuarina equisetifolia. At the same time, twig samples from a male tree and seeds from all potential pollen recipients will be collected from the same plantation. The collected progenies and twig samples will be subjected to paternity analysis using SSR technique, and pollen dispersal distances and patterns in plantation will be analyzed based on determining the pollen donors of all progenies. One potted grafted male tree with blooming flowers will be set as the focal tree, potted grafted female ramets with blooming flowers will be arranged around the focal tree in different distances and directions respectively, and pollen capturers are fixed in each ramets. Pollen dispersal patterns, pollen densities and pollen limitation values in different distances and directions around the focal tree will be measured, and their effects on reproductive success and progeny fitness of C. equisetifolia will be determined. Results from this study will provide important theoretical and practical values on setting buffer zones, allocating male and female individuals, improving seed yield and quality during establishment and management of C. equisetifolia seed orchards.

花粉是植物主要的基因流载体，其散布的距离和模式不仅能改变植物居群的遗传结构与多样性，还会影响植物的生殖成功和子代适应性。文献表明，国内外主要在居群尺度上对天然分布植物开展花粉散布研究，在外来树种人工林的个体水平上对花粉散布研究还鲜有报道。本项目以短枝木麻黄为研究对象，在人工林内采集雌株的种子和该雌株周围雄株的叶样，同时采集雄株的叶样和该雄株周围雌株的种子，应用基于SSR分子标记的父本分析技术确定种子的父本来源，揭示短枝木麻黄在自由授粉条件下的花粉散布距离与模式；在苗圃中，以开花的嫁接盆栽雄株为中心，在不同方向和距离放置开花的嫁接盆栽雌株和设置花粉捕捉器，结合气候因子观测数据，研究花粉的散布模式、不同距离和方向的花粉密度和花粉限制值等，探讨它们对生殖成功和子代适应性的影响。研究结果将对木麻黄种子园营建中花粉隔离带的设置、雌雄株的配置、种子产量和质量的提高等有重要的理论价值和实践意义。

木麻黄在我国华南沿海的防护林建设中起到不可替代的作用，但现阶段以无性系为主的木麻黄防护林在抗病性、抗台风等方面显著弱于用实生苗建立的木麻黄防护林，尤其是在沿海前沿基干林带和困难立地的防护林建设上木麻黄实生苗的应用更占优势。因此需要建立木麻黄种子园为防护林建设提供经过遗传改良的优质种子，但迄今为止还没有木麻黄种子园营建方面的理论和实践经验可供借鉴。本项目的目的是研究木麻黄的花粉散布距离与模式，花粉限制对短枝木麻黄的生殖成功和种子产量和质量的影响等基础理论和技术，为木麻黄种子园的营建提供理论指导和技术支持。. 研究结果表明，短枝木麻黄花粉散布的有效距离是0-70 m，平均散布距离为28.8 m，母树的子代中有96.4%的花粉来源位于母树60 m范围内，且花粉散布没有明显受到风向的影响，母株附近的雄株花粉在花粉竞争中具有较明显的优势；花粉散布距离对子代的适应性和遗传多样性没有显著影响，同时子代（种子和小苗）的适应性（种子发芽势、种子活力指数、苗木质量指数、苗木生长速度、干物质质量等）与子代的遗传多样也无显著的相关关系；花粉限制条件下的子代群体虽然在平均等位基因数、有效等位基因数、观测杂合度、期望杂合度、多态性信息含量、Shannon's信息指数和Nei's遗传多样性指数都略低于非花粉限制子代群体，但均达不到统计学上的显著差异，表明在花粉限制条件下并不会显著降低短枝木麻黄子代群体的遗传多样性。. 这些研究结果表明，因为木麻黄花粉散布的有效距离较近，因此木麻黄种子园的选址时不需要过宽的隔离带来防止外来花粉的污染（300-500 m已足够）；雌株附近的雄株的花粉在花粉竞争中具有明显优势，表明在种子园建设时需要合理配置雌株和雄株，确保不同雌雄株间具有充分的授粉机会；花粉限制对种子产量产生一定的影响，但对子代适应性和遗传多样性没有显著的影响。