不同光环境对麻栎和刺槐幼苗生长和光合特征的影响

通过搭建遮阳棚设置3个光照强度,模拟森林幼苗生长的林缘、林窗和林下光环境,研究麻栎和刺槐幼苗形态结构、光合特性、生物量积累及其分配对不同光照强度的响应。结果表明,极度弱光环境限制了幼苗的株高、基径、总叶面积、冠面积、叶面积指数和总叶数等形态指标的增长,与全光环境相比,适度遮荫有利于幼苗的形态生长,光照对麻栎形态的异速生长曲线影响较小,刺槐较麻栎的曲线变化更明显一些,弱光降低了异速生长指数。随遮荫程度的增加,麻栎的净光合速率、蒸腾速率、气孔导度逐渐降低,刺槐的净光合速率则在适度遮荫下最大,两者的光能利用效率均显著增大,水分利用效率先升后降。随光照强度的减弱,麻栎各器官的生物量积累降低,叶面积比率的增加和根冠比的减少有利于增加光能的捕获,而刺槐的生物量积累和分配则在适度遮荫下达到最优;各叶绿素含量均显著上升,而叶绿素a/b则逐渐下降。麻栎和刺槐显示出不同的生存策略和光利用策略,在一定程度上可以揭示它们在阔叶林群落中不同的演替地位。

Effects of light intensity on growth and photosynthesis of seedlings of Quercus acutissima and Robinia pseudoacacia

A light control treatment with three light gradients (100%, 66% and 10% of natural light) was conducted to simulate the light conditions of the forest edge, forest gap and understory where seedlings grow. This was achieved by building shade shelters covered by woven black nylon nets. The purpose of this experiment was to study the morphology, photosynthetic characters, biomass accumulation and allocation of Quercus acutissima and Robinia pseudoacacia seedlings in response to diverse gradients of light. The results showed that morphological features of plant height, stem diameter, total leaf area, crown area, leaf area index and total leaf number were seriously inhibited under severe shade conditions, while moderate shade treatment was suitable to growth of seedlings. Effects of light on allometric trajectories of morphology were small in Q. acutissima but more obvious in R. pseudoacacia as the low light depressed the exponents of functions. With a decrease of light, net photosynthetic rate, transpiration rate and stomatal conductance of Q. acutissima were decreased, while the maximum photosynthetic rate of R. pseudoacacia occurred with moderate shade treatment. Light use efficiency in both species increased when the light intensity was restricted. The water use efficiency was the highest under moderate shade treatment, but lowest under severe shade conditions. The trends of biomass accumulation were consistent with those of photosynthetic parameters. Biomass accumulation in each organ was limited by the deficit of light for Q. acutissima, but the best status of biomass accumulation and allocation for R. pseudoacacia was found under moderate shade treatments. Higher leaf area index and lower root to shoot ratio could increase the capacity of light capture. Also, the total content of chlorophyll increased and Chl a/b decreased with decreasing light intensity. The different strategies of growth and light utilization between Q. acutissima and R. pseudoacacia might reveal, to a certain extent, their status in the succession of deciduous broadleaved communities.