Valladares Fernando, Hernández Libertad G, Dobarro Iker, García-Pérez Cristina, Sanz Rubén, Pugnaire Francisco I
Centro de Ciencias Medioambientales C.S.I.C. Serrano 115 dpdo, Madrid E-28006, Spain.
Ann Bot. 2003 Apr;91(5):577-84. doi: 10.1093/aob/mcg059.
Different plant species and organs within a plant differ in their plastic response to light. These responses influence their performance and survival in relation to the light environment, which may range from full sunlight to deep shade. Plasticity, especially with regard to physiological features, is linked to a greater capacity to exploit high light and is usually low in shade-tolerant species. Among photosynthetic organs, green stems, which represent a large fraction of the total photosynthetic area of certain species, are hypothesized to be less capable of adjustment to light than leaves, because of biomechanical and hydraulic constraints. The response to light by leaves and stems of six species of leguminous, green-stemmed shrubs from dry and high-light environments was studied by growing seedlings in three light environments: deep shade, moderate shade and sun (3, 30 and 100 % of full sunlight, respectively). Survival in deep shade ranged from 2 % in Retama sphaerocarpa to 74 % in Ulex europaeus. Survival was maximal at moderate shade in all species, ranging from 80 to 98 %. The six species differed significantly in their ratio of leaf to total photosynthetic area, which influenced their light response. Survival in deep shade increased significantly with increasing ratio of leaf to total photosynthetic area, and decreased with increasing plasticity in net photosynthesis and dark respiration. Responses to light differed between stems and leaves within each species. Mean phenotypic plasticity for the variables leaf or stem specific mass, chlorophyll content, chlorophyll a/b ratio, and carotenoid to chlorophyll ratio of leaves, was inversely related to that of stems. Although mean plasticity of stems increased with the ratio of leaf to total photosynthetic area, the mean plasticity of leaves decreased. Shrubs with green stems and a low ratio of leaf to total photosynthetic area are expected to be restricted to well-lit habitats, at least during the seedling stage, owing to their inefficient light capture and the low plasticity of their stems.
不同的植物物种以及植物体内的不同器官对光照的可塑性反应存在差异。这些反应影响它们在光照环境中的表现和生存，光照环境范围可能从全日照到深度遮荫。可塑性，尤其是生理特征方面的可塑性，与利用强光的能力更强相关，而在耐荫物种中通常较低。在光合器官中，绿色茎干占某些物种总光合面积的很大一部分，由于生物力学和水力限制，据推测其对光照的调节能力不如叶片。通过在三种光照环境下培育幼苗，研究了六种来自干旱和强光环境的豆科绿色茎干灌木的叶片和茎干对光照的反应：深度遮荫、中度遮荫和阳光照射（分别为全日照的3%、30%和100%）。在深度遮荫下的存活率从圆果骆驼刺的2%到欧洲刺柏的74%不等。所有物种在中度遮荫下存活率最高，范围为80%至98%。这六个物种的叶面积与总光合面积之比存在显著差异，这影响了它们的光照反应。在深度遮荫下的存活率随着叶面积与总光合面积之比的增加而显著增加，随着净光合和暗呼吸可塑性的增加而降低。每个物种的茎干和叶片对光照的反应不同。叶片的叶或茎比质量、叶绿素含量、叶绿素a/b比以及类胡萝卜素与叶绿素比等变量的平均表型可塑性与茎干的平均表型可塑性呈负相关。虽然茎干的平均可塑性随着叶面积与总光合面积之比的增加而增加，但叶片的平均可塑性却降低了。由于其低效的光捕获能力和茎干的低可塑性，预计绿色茎干且叶面积与总光合面积之比低的灌木至少在幼苗期将局限于光照良好的生境。
