Avalos Gerardo, Mulkey Stephen S
Department of Biology, University of Missouri-St. Louis, 8001 Natural Bridge Road, St. Louis, MO 63121-4499, USA e-mail:
Department of Botany, University of Florida, P.O. Box 118526, Gainesville, FL 32611-8526, USA, , , , , , US.
Oecologia. 1999 Sep;120(4):475-484. doi: 10.1007/s004420050880.
Tropical plant canopies show abrupt changes in light conditions across small differences in spatial and temporal scales. Given the canopy light heterogeneity, plants in this stratum should express a high degree of plasticity, both in space (allocation to plant modules as a function of opportunity for resource access) and time (photosynthetic adjustment to temporal changes in the local environment). Using a construction crane for canopy access, we studied light acclimation of the liana Stigmaphyllon lindenianum to sun and shade environments in a tropical dry forest in Panama during the wet season. Measured branches were randomly distributed in one of four light sequences: high- to low-light branches started the experiment under sun and were transferred to shade during the second part of the experiment; low- to high-light branches (LH) were exposed to the opposite sequence of light treatments; and high-light and low-light controls , which were exposed only to sun and shade environments, respectively, throughout the experiment. Shade branches were set inside enclosures wrapped in 63% greenhouse shade cloth. After 2 months, we transferred experimental branches to opposite light conditions by relocating the enclosures. Leaf mortality was considerably higher under shade, both before and after the transfer. LH branches reversed the pattern of mortality by increasing new leaf production after the transfer. Rates of photosynthesis at light saturation, light compensation points, and dark respiration rates of transferred branches matched those of controls for the new light treatment, indicating rapid photochemical acclimation. The post-expansion acclimation of sun and shade foliage occurred with little modification of leaf structure. High photosynthetic plasticity was reflected in an almost immediate ability to respond to significant changes in light. This response did not depend on the initial light environment, but was determined by exposure to new light conditions. Stigmaphyllon responded rapidly to light changes through the functional adjustment of already expanded foliage and an increase in leaf production in places with high opportunity for carbon gain.
热带植物冠层在空间和时间尺度上的微小差异会导致光照条件的突然变化。鉴于冠层光照的异质性，该层次的植物在空间（根据获取资源的机会分配植物模块）和时间（对当地环境时间变化的光合调节）上都应表现出高度的可塑性。我们利用一台建筑起重机进入冠层，研究了巴拿马热带干旱森林中藤本植物林登氏 stigmaphyllon 在雨季对阳光和遮荫环境的光适应情况。测量的枝条随机分布在四种光照序列之一中：从高光到低光的枝条在实验开始时处于阳光下，在实验的第二部分转移到遮荫处；从低光到高光的枝条（LH）接受相反的光照处理序列；以及高光和低光对照，它们在整个实验过程中分别仅暴露于阳光和遮荫环境。遮荫枝条设置在包裹有63%温室遮荫布的围栏内。2个月后，我们通过重新安置围栏将实验枝条转移到相反的光照条件下。在转移前后，遮荫条件下的叶片死亡率都显著更高。LH枝条在转移后通过增加新叶产量扭转了死亡率模式。转移枝条在光饱和时的光合速率、光补偿点和暗呼吸速率与新光照处理的对照相匹配，表明快速的光化学适应。阳生叶和阴生叶在叶片结构几乎没有改变的情况下发生了扩展后的适应。高光合可塑性体现在几乎能立即对光照的显著变化做出反应。这种反应不依赖于初始光照环境，而是由暴露于新的光照条件决定。Stigmaphyllon 通过对已展开叶片的功能调节以及在碳获取机会高的地方增加叶片产量，对光照变化做出了快速反应。
