不同光环境下紫椴幼树树冠结构的可塑性响应

Response of structural plasticity of Tilia amurensis sapling crowns to different light conditions.

从冠形、侧枝和叶片在树冠中的空间分布角度对天然更新紫椴幼树的树冠结构进行了论述 ,认为紫椴幼树树冠对光照条件的变化有显著的可塑性响应 .强光通过抑制主干的生长促进了侧枝的分化 ,庇荫则通过抑制 1级侧枝的生长促进了侧枝的再分枝 .随着光照水平的降低 ,紫椴幼树的数量叶片密度显著降低 ,且叶片逐渐集中于冠上层 .林冠下的紫椴幼树通过这种侧枝和叶片的分布格局 ,在形态上提高其对光的截获能力 .在适度庇荫环境中 ,紫椴幼树垂直生长采取演替先锋种的“避荫”对策 ,侧枝生长采取中等耐荫种的“掠光”对策 ;在弱光环境中 ,紫椴幼树则采取典型的忍耐适应行为 .这种树冠结构的变化是提高紫椴幼树对光的截获能力的一种有益适应 .

This paper studied the crown structure of Tilia amurensis saplings,e.g.the shape of crown,and the distribution of branch and leaf.It is shown that the crown structure of the saplings was modified plastically in response to different light conditions.The differentiation of the first order branches was promoted by strong radiation,due to the bole growth being inhibited under high light condition,whereas the bifurcation density of the first order branches whose growth was inhibited by shading was promoted in under canopy environment.The quantitative leaf densities of the saplings obviously decreased with the decrease of light level,while their leaves tented to distribute in upper corwn.The interception of the saplings was enhanced by the distribution pattern of branches and leaves in crown.Under adequate shade condition,the saplings had the strategy of shade avoidance of pioneer species in upward growth,and had the strategy of light forage of moderate shade tolerance in horizontal branch growth.The saplings expressed typically shade tolerant under weak light condition.Such a change of crown structure was an advantageous adaptation for enhancing light interception.