表型可塑性对木本植物树冠结构与发育的影响

作为一组固生生物 ,树木具备一种独特的生存能力来适应在漫长生长过程中发生的环境变化。正是因为这样的原因 ,树木的许多生物学特性 ,如分枝习性与树冠结构 ,代表了树木的生长“蓝图”或基因型与其生长环境及历史的互作关系。遗传因子通过突变 ,染色体重组、基因重复 ,易位与互换等过程形成树木发育成固定的结构。早期形态学家已认识到 ,树木存着大量的形态与发育方面的重复 ,利用这些重复的分化 ,许多热带树种可以被划分成少数几组形态。类似的工作已用在温带树木的结构分析上。但是 ,尽管发展这样的一个分类机制是很容易的 ,然而实际的应用却非常困难 ,这是因为在相同的树木类别内 ,甚至在相同树种内 ,存在着巨大的表型分化。不同的环境或发育过程会使具有相同基因型的树木产生不同的结构 ,由此可见其影响和遗传影响同样复杂环境对树木结构的影响称为表型可塑性。通过缓解自然选择的效应 ,表型可塑性对提高植物适应能力具有重要作用。如果表型可塑性存在遗传变异 ,那么 ,具有不同可塑性的群体会产生进化。表型可塑性亦可用于分析由环境引起的性状相关 ,例如环境能导致性状相关在方向与大小上的变化。基因型与环境互作的结果导致有机体的发育以外遗传的系统的改变 ,产生所谓的异时性生长 (heterochron

HOW PHENOTYPIC PLASTICITY AFFECTS CROWN ARCHITECTURE AND DEVELOPMENT IN WOODY PLANTS

Tree architecture has been recognized to be the consequence of interactions between a tree's blue print or genotype,its environment and its developmental history.In tropical trees and many temperate zone trees,tree architecture includes two contrasting branching types,sylleptic and proleptic branches.Sylleptic branches develop from lateral buds of the main stem without an intervening period of dormancy,whereas proleptic branches develop from lateral buds of the main stem with an intervening period of dormancy.Although these two branch types can occur in the same tree,they normally display marked discrepancies in morphogensis and the extent to which they phenotypically respond to environmental changes.It has been recognized that the phenotypic plasticity of sylleptic branching plays an important role in determining tree growth, architecture and adaptation for many temperate zone woody plants.In this article,we further examine control mechanisms for the phenotypic plasticity of sylleptic branches at the environmental,developmental and genetic levels.