不同光环境下木荷幼苗树冠结构的可塑性响应

从冠形、侧枝和叶片在树冠中的空间分布等方面对天然更新木荷（Schima superba Gardn．et Champ．）幼苗的树冠结构进行了研究，认为木荷幼苗的树冠对光照条件的变化有显著的可塑性响应。随着光照水平的提高，幼苗树冠由阔、松散型向相对紧密、窄冠型发展，表明木荷幼苗对不同光照环境有较强的适应能力。木荷幼苗在强光环境下产生短枝，在适度荫庇条件下侧枝和主枝同时向上方和侧方伸长生长；在强度遮阴条件下，侧枝发生强烈的伸长生长并发生强烈的分枝行为，同时在不同自然环境条件下幼苗的叶片密度由全光、林隙到林冠下逐渐提高。随着光照水平的减弱，1级侧枝密度逐渐降低，分枝（2级侧枝和3级侧枝）强度却逐渐增大，且侧枝在树冠上的分布有向匕集中的趋势。

Response of structural plasticity of Schima superba sapling crown to different light conditions

The crown structure of Schima superba Gardn. et Champ. saplings were studied from the shape of crown, the distribution of branch and leaf, etc. It showed that the crown structure of saplings was modified plastically in response to different light conditions. The sapling crown grew from broader to smaller with the increase of light level. The sapling branches were the shortest under high light condition, but grew horizontally or upward under adequate shade condition. And while in under-canopy environment, the branches were elongated and divaricated intensely. The leaf density of the saplings increased with the decrease of light level. When light level decreased, the density of the first order branches decreased, whereas that of the second and the third branches increased, and the distribution of lateral branches in crown tended up to gather on higher stratum.