Valladares F, Allen Mitchell T, Pearcy Robert W
Centro de Ciencias Medioambientales, CSIC, Serrano 115 dpdo, 28040 Madrid, Spain, , , , , , ES.
Section of Evolution and Ecology, Division of Biological Sciences, University of California, Davis, CA 95616, USA, , , , , , US.
Oecologia. 1997 Aug;111(4):505-514. doi: 10.1007/s004420050264.
We examined in the field the photosynthetic utilization of fluctuating light by six neotropical rainforest shrubs of the family Rubiaceae. They were growing in three different light environments: forest understory, small gaps, and clearings. Gas exchange techniques were used to analyse photosynthetic induction response, induction maintenance during low-light periods, and lightfleck (simulated sunfleck) use efficiency (LUE). Total daily photon flux density (PFD) reaching the plants during the wet season was 37 times higher in clearings than in the understory, with small gaps exhibiting intermediate values. Sunflecks were more frequent, but shorter and of lower intensity in the understory than in clearings. However, sunflecks contributed one-third of the daily PFD in the understory. Maximum rates of net photosynthesis, carboxylation capacity, electron transport, and maximum stomatal conductance were lower in understory species than in species growing in small gaps or clearings, while the reverse was true for the curvature factor of the light response of photosynthesis. No significant differences were found in the apparent quantum yield. The rise of net photosynthesis during induction after transfer from low to high light varied from a hyperbolic shape to a sigmoidal increase. Rates of photosynthetic induction exhibited a negative exponential relationship with stomatal conductance in the shade prior to the increase in PFD. Leaves of understory species showed the most rapid induction and remained induced longer once transferred to the shade than did leaves of medium- or high-light species. LUE decreased rapidly with increasing lightfleck duration and was affected by the induction state of the leaf. Fully induced leaves exhibited LUEs up to 300% for 1-s lightflecks, while LUE was below 100% for 1-80 s lightflecks in uninduced leaves. Both induced and uninduced leaves of understory species exhibited higher LUE than those of species growing in small gaps or clearings. However, most differences disappeared for lightflecks 10 s long or longer. Thus, understory species, which grew in a highly dynamic light environment, had better capacities for utilization of rapidly fluctuating light than species from habitats with higher light availability.
我们在野外研究了茜草科六种新热带雨林灌木对波动光的光合利用情况。它们生长在三种不同的光照环境中：森林林下、小间隙和林中空地。采用气体交换技术分析光合诱导响应、弱光期的诱导维持以及光斑（模拟太阳光斑）利用效率（LUE）。雨季期间到达植物的每日总光子通量密度（PFD）在林中空地比林下高37倍，小间隙呈现中间值。林下的太阳光斑更频繁，但比林中空地更短且强度更低。然而，太阳光斑在林下贡献了每日PFD的三分之一。林下物种的净光合最大速率、羧化能力、电子传递和最大气孔导度低于生长在小间隙或林中空地的物种，而光合作用光响应的曲率因子则相反。表观量子产率未发现显著差异。从低光转移到高光后诱导期间净光合作用的上升从双曲线形状到S形增加不等。在PFD增加之前，光合诱导速率与遮荫条件下的气孔导度呈负指数关系。林下物种的叶片显示出最快的诱导，并且一旦转移到遮荫条件下，比中光或高光物种的叶片保持诱导状态的时间更长。LUE随着光斑持续时间的增加而迅速下降，并受叶片诱导状态的影响。完全诱导的叶片对1秒光斑的LUE高达300%，而未诱导叶片对1 - 80秒光斑的LUE低于100%。林下物种的诱导和未诱导叶片均比生长在小间隙或林中空地的物种表现出更高的LUE。然而，对于10秒及更长时间的光斑，大多数差异消失。因此，生长在高度动态光照环境中的林下物种比来自光照条件更好栖息地的物种具有更好的利用快速波动光的能力。
