The whole-plant economic spectrum concept predicts that leaf and root traits evolve in coordination to cope with environmental stresses. However, this hypothesis is difficult to test in many species because their leaves and roots are exposed to different environments, above- and below-ground. In epiphytes, both leaves and roots are exposed to the atmosphere. Thus, we suspect there are consistent water conservation strategies in leaf and root traits of epiphytes due to similar selection pressures. Here, we measured the functional traits of 21 species in the genus Dendrobium, which is one of the largest epiphytic taxa in the family Orchidaceae, and used phylogenetically independent contrasts to test the relationships among traits, and between traits and the environment. Our results demonstrate that species with a thicker velamen tended to have thicker roots, a thicker root cortex and vascular cylinder, and a larger number of vessels in the root. Correspondingly, these species also had higher leaf mass per area, and thicker leaf lower cuticles. Leaf and root traits associated with water conservation showed significantly positive relationships. The number of velamen layers, leaf density and the ratio of vascular cylinder radius to root radius were significantly affected by the species’ differing environments. Thus, traits related to water conservation and transport may play an important role in helping Dendrobium cope with the cool and dry conditions found at high elevations. These findings confirmed the hypothesis that leaf and root traits have evolved in coordination, and also provide insights into trait evolution and ecological adaptation in epiphytic orchids.

中文翻译：

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石斛兰（兰科）叶和根解剖性状的相关进化。

全植物经济谱概念预测叶和根性状协调进化以应对环境压力。然而，这一假设很难在许多物种中得到检验，因为它们的叶子和根暴露在不同的环境中，地上和地下。在附生植物中，叶子和根都暴露在大气中。因此，我们怀疑由于相似的选择压力，附生植物的叶和根性状存在一致的保水策略。在这里，我们测量了石斛兰属（兰科最大的附生类群之一）中21 个物种的功能性状，并使用系统发育独立对比来测试性状之间以及性状与环境之间的关系。我们的结果表明，根部较厚的物种往往具有较厚的根、较厚的根皮层和维管柱，以及根中较多的血管。相应地，这些物种也具有较高的单位面积叶质量和较厚的叶下角质层。与节水相关的叶和根性状表现出显着的正相关关系。不同物种的不同环境对表皮层数、叶片密度以及维管柱半径与根半径之比的影响显着。因此，与节水和运输相关的特性可能在帮助石斛兰应对高海拔地区凉爽和干燥的条件方面发挥重要作用。这些发现证实了叶和根性状协调进化的假设，也为附生兰花的性状进化和生态适应提供了见解。