遮阴对三种木兰科幼苗生长和光合特性的影响

为探讨观光木、山白兰和灰木莲三种木兰科植物对不同光环境的光合适应机制,该文以其幼苗为材料,设置透光率分别为100% NS、72.3% NS、48.6% NS、24.9% NS的四种光照处理,测定其光合特性参数、生物量分配比例、叶绿素含量等,研究不同遮阴处理对其生长和光合作用的影响。结果表明:(1)过强或过弱的光照环境限制了幼苗株高及地径的生长,与全光照相比,72.3% NS有利于幼苗的形态生长。(2)随着遮阴程度的增加,观光木、山白兰和灰木莲幼苗的最大光合速率、光补偿点、光饱和点、暗呼吸速率、蒸腾速率逐渐降低,叶绿素含量增加,水分利用效率先升后降。(3)随着光强的减弱,观光木和山白兰地上部分的生物量积累增加,灰木莲的根生物量积累增加。(4)观光木的比叶面积随着遮阴程度的增加而先增后减; 灰木莲的比叶面积显著减小; 山白兰的比叶面积差异不显著; 观光木、山白兰和灰木莲对低光环境响应和适应的差异主要表现在生物量分配比例及叶的形态特征上。综上结果认为,72.3% NS最有利于幼苗的生长,观光木、山白兰和灰木莲在遮阴条件下可以通过降低P_max、LSP、LCP、R_d、T_r来增加叶绿素含量,适当调整生物量分配比例来增大光合能力,在中度遮阴时能增加水分利用效率、株高、地径来增大光合能力。

Effects of shading on growth and photosynthetic characteristics of three Magnoliaceae seedlings

In order to explore the light intensity adaptation of three Magnoliaceae species, including Tsoongiodendron odorum, Michelia alba and Manglietia glauca to different light conditions, the seedlings were grown under four light regimes(100%, 72.3%, 48.6%, 24.9% of natural sunlight). The photosynthetic characteristic parameters, biomass distribution ratio and chlorophyll contents were measured. In addition, the effects of light intensity on seedling photosynthetic efficiency and their growth were analyzed. The results were as follows:(1)Seedlings vertical and diametral growth were seriously inhibited under either excessive shadings or excessive sunlight. 72.3% natural sunlight was found to be optimal for seedling growth.(2)With the light intensity increasing, maximum photosynthetic rate(P_max), light compensation point(LCP), light saturation point(LSP), respiration rate(R_d), and transpiration rate(T_r)of Tsoongiodendron odorum, Michelia alba and Manglietia glauca decreased. Chlorophyll contents increased, while the water use efficiency reached its highest value under moderate shade treatment, but lowest under severe shade conditions.(3)Under low light conditions, the aboveground biomass fraction of Tsoongiodendron odorum and Michelia alba increased, while the belowground biomass of Manglietia glauca was increased.(4)With the light intensity decreasing, the specific leaf area(SLA)of Tsoongiodendron odorum increased firstly and then decreased, SLA of Manglietia glauca decreased significantly, those of Michelia alba was not significantly different. The results suggested that the differences of response and adaptation of Tsoongiodendron odorum, Michelia alba and Manglietia glauca to low light environment were mainly observed in aboveground/belowground biomass distribution ratio and the morphological characteristics of leaves. Tsoongiodendron odorum, Michelia alba and Manglietia glauca may increase their photosynthetic capacity by increasing chlorophyll contents, reducing P_max, LSP, LCP, R_d, T_r, adjusting the aboveground/belowground biomass distribution ratio appropriately under shade condition. 72.3% natural sunlight was found to be optimal for seedling growth.