中国沙棘人工林萌蘖能力对平茬高度的响应规律及其激素调控机制

Hippophae rhamnoides ssp. sinensis is an excellent and multiple-purpose tree species. With their strong clone propagation ability and eternal potential, it has played an important and peculiar role in revegetation in the North China arid and semi-arid areas. However, many plantations in their modern distributive centers began to premature aging even die in the recent years. The effective way to resolve this problem is stumping, which have been proven effective in other tree species. It has been reported that stumping is relevant to age, season and height. However, few attempts have been made in this area in Hippophae rhamnoides ssp. sinensis. On the other hand, the sprouting mechanism research was more confined to physiology and ecology level, and few attempts have been made on phytohormone level, let alone at gene level. In view of the key and important role of phytohormone that played on plant regeneration, here we will designing a stumping experiment to study the sprouting ability responsible for stumping height. On the basis of above results, we will mainly study the relationship between sprouting ability and endogenous phytohormone, including relationship between sprouting ability and content, distribution and ratio of Auxin, Gibberellic Acid, Cytokinin, Abscisic acid and Strigolactones. In addition, we will also study the above relationship at the gene expression level. Our final object is to clarify the mechanism of sprouting ability response to stumping height at the phytohormone level. This research will expand the field of regeneration study and will provide theoretical basis for plantation regeneration of Hippophae rhamnoides ssp. sinensis.

中国沙棘是优良的多用途树种，且克隆繁殖能力极强，具有“独木成林”和“永生”的潜力，在我国北方旱区植被恢复中具有重要而特殊的作用，但其人工林近年发生了大面积早衰甚至死亡现象，解决这一问题最为有效的途径是通过平茬促萌实施更新。平茬促萌效果与平茬年龄、季节、高度等因素息息相关，但关于中国沙棘平茬高度问题未见报道。另一方面，林木平茬促萌机制的研究几乎局限于生理生态层次，激素调控问题只见零星报道，基因表达机制更是罕见报道。鉴于内源激素在萌蘖调控中的关键作用和纽带作用，本项目试图在摸清萌蘖能力对平茬高度的响应规律基础上，以生长素、赤霉素、细胞分裂素、脱落酸、独脚金内酯的含量、比例、分布、动态与萌蘖能力的关系分析为核心，从生态适应、激素特征、基因表达及其相互关系角度探讨萌蘖能力的激素调控机制，为完善森林萌蘖更新的激素调控机制研究提供新案例，为沙棘人工林的平茬促萌更新提供理论依据。

中国沙棘是我国“三北防护林”地区重要而特殊的造林树种，用途多样、萌蘖能力极强，具有“独木成林”和“永生不灭”的潜力，但人工林近年来发生大面积早衰。平茬（促萌）更新是解决这一问题最为有效的途径，相关机制研究却局限于生理生态层次。为探讨其分子调控机制，基于不同平茬高度（留桩0、10、20cm以及不平茬）田间试验和室内测试结果，分析萌蘖能力、激素特征、基因表达对平茬高度和平茬时间的响应规律及其因果关系。结果表明：（1）平茬显著促进萌蘖发生和生长、提高种群稳定性，但不同平茬高度之间存在明显差异。随着平茬高度的增大，伐桩萌蘖存活率、根系萌蘖数量以及萌蘖生长、克隆扩散、生物积累能力的再生率先升后降（或先升后稳），根据回归方程求出最有利于种群快速恢复的平茬高度为10.0cm~12.0cm。（2）平茬提高了 IAA/ABA、 ZR/ABA、GA3/ABA 比值以及萌蘖初期的IAA、ZR、GA3含量，降低ABA含量。由于萌蘖（发生及生长）能力与 IAA、ZR、GA3 含量以及 IAA/ABA、ZR/ABA、 GA3/ABA 比值呈正相关，与ABA含量呈负相关，因此平茬使萌蘖能力显著提升。（3）平茬后，激素合成、代谢、转运基因通过表达改变首先做出响应，并通过激素合成、代谢、转运基因表达-激素特征-激素信号转导基因表达-萌蘖能力-种群稳定性顺序调控而依次发生改变。由于基因表达、激素特征对不同平茬高度的响应存在差异，因此导致萌蘖能力及种群稳定性在不同平茬高度之间形成差异。这些结果将平茬（促萌）更新机制研究从生理生态层次拓展到分子层次、将平茬（促萌）更新效果研究从个体水平提升到种群水平，为类似研究提供了新案例甚至新思路；根据回归方程求出的最佳平茬高度，具有更加可靠的科学依据和实用价值（与以往的对比分析相对而言）。