Mason Chase M, Donovan Lisa A
Department of Plant Biology, University of Georgia, Athens, Georgia, 30602.
Evolution. 2015 Oct;69(10):2705-20. doi: 10.1111/evo.12768. Epub 2015 Sep 29.
The leaf economics spectrum (LES) describes a major axis of plant functional trait variation worldwide, defining suites of leaf traits aligned with resource-acquisitive to resource-conservative ecological strategies. The LES has been interpreted to arise from leaf-level trade-offs among ecophysiological traits common to all plants. However, it has been suggested that the defining leaf-level trade-offs of the LES may not hold within specific functional groups (e.g., herbs) nor within many groups of closely related species, which challenges the usefulness of the LES paradigm across evolutionary scales. Here, we examine the evolution of the LES across 28 species of the diverse herbaceous genus Helianthus (the sunflowers), which occupies a wide range of habitats and climate variation across North America. Using a phylogenetic comparative approach, we find repeated evolution of more resource-acquisitive LES strategies in cooler, drier, and more fertile environments. We also find macroevolutionary correlations among LES traits that recapitulate aspects of the global LES, but with one major difference: leaf mass per area is uncorrelated with leaf lifespan. This indicates that whole-plant processes likely drive variation in leaf lifespan across Helianthus, rather than leaf-level trade-offs. These results suggest that LES patterns do not reflect universal physiological trade-offs at small evolutionary scales.
叶经济谱（LES）描述了全球植物功能性状变异的一个主要轴，定义了与从资源获取型到资源保守型生态策略相关的一系列叶性状。LES被解释为源于所有植物共有的生态生理性状在叶片水平上的权衡。然而，有人提出，LES在特定功能组（如草本植物）内或许多近缘物种组内可能并不成立，这对LES范式在进化尺度上的实用性提出了挑战。在这里，我们研究了28种不同的草本向日葵属植物（向日葵）的LES进化情况，该属植物在北美占据了广泛的栖息地和气候变异范围。使用系统发育比较方法，我们发现在更凉爽、干燥和肥沃的环境中，更倾向于资源获取型的LES策略会反复进化。我们还发现LES性状之间的宏观进化相关性概括了全球LES的一些方面，但有一个主要区别：单位面积叶质量与叶寿命不相关。这表明，整个植株水平的过程可能驱动了向日葵属植物叶寿命的变异，而不是叶片水平的权衡。这些结果表明LES模式在小进化尺度上并不反映普遍的生理权衡。
