Data from: Causes of ecological gradients in leaf margin entirety: Evaluating the roles of biomechanics, hydraulics, vein geometry, and bud packing

PREMISE OF THE STUDY: A recent commentary by Edwards et al. (Am. J. Bot. 103: 975–978) proposed that constraints imposed by the packing of young leaves in buds could explain the positive association between non-entire leaf margins and latitude but did not thoroughly consider alternative explanations. METHODS: We review the logic and evidence underlying six major hypotheses for the functional significance of marginal teeth, involving putative effects on (1) leaf cooling, (2) optimal support and supply of the areas served by major veins, (3) enhanced leaf-margin photosynthesis, (4) hydathodal function, (5) defense against herbivores, and (6) bud packing. KEY RESULTS: Theoretical and empirical problems undermine all hypotheses except the support–supply hypothesis, which implies that thinner leaves should have non-entire margins. Phylogenetically structured analyses across angiosperms, the El Yunque flora, and the genus Viburnum all demonstrate that non-entire margins are indeed more common in thinner leaves. Across angiosperms, the association of leaf thickness with non-entire leaf margins is stronger than that of latitude. CONCLUSION: We outline a synthetic model showing how biomechanics, hydraulics, vein geometry, rates of leaf expansion, and length of development within resting buds, all tied to leaf thickness, drive patterns in the distribution of entire vs. non-entire leaf margins. Our model accounts for dominance of entire margins in the tropics, Mediterranean scrub, and tundra, non-entire margins in cold temperate deciduous forests and tropical vines and early-successional trees, and entire leaf margins in monocots. Spinose-toothed leaves should be favored in short-statured evergreen trees and shrubs, primarily in Mediterranean scrub and related semiarid habitats.

本研究的研究前提：爱德华兹（Edwards）等人发表于《美国植物学杂志（American Journal of Botany）》103卷975-978页的近期评论提出，芽内幼叶排列所带来的约束限制，可以解释非全缘叶缘（non-entire leaf margins）与纬度之间的正相关关系，但该研究未充分考虑其他潜在解释路径。
研究方法：本研究梳理了关于叶缘齿状特征功能意义的六大主流假说背后的逻辑与证据，这些假说分别涉及：（1）叶片降温效应；（2）主脉供养区域的最优支撑与养分供给；（3）增强叶缘光合能力；（4）排水孔（hydathode）功能；（5）抵御植食性动物；（6）芽内幼叶排列。
主要研究结果：理论与实证层面的问题均推翻了除支撑-供养假说之外的所有假说，该假说预示薄型叶片更易具备非全缘叶缘。针对被子植物、埃尔云克植物区系以及荚蒾属（Viburnum）开展的系统发育结构化分析均证实，薄型叶片确实更易出现非全缘叶缘。在被子植物类群中，叶片厚度与非全缘叶缘的相关性强于其与纬度的相关性。
研究结论：本研究构建了一个综合模型，阐明了与叶片厚度紧密关联的生物力学、水力特性、脉管几何结构、叶片扩张速率以及休眠芽内发育时长，如何共同驱动全缘与非全缘叶缘的分布格局。该模型能够解释以下分布规律：热带地区、地中海灌丛以及苔原带以全缘叶缘为主；寒温带落叶林、热带藤本与早期演替树种则以非全缘叶缘为主；而单子叶植物（monocots）则多具备全缘叶缘。具棘状齿的叶片更适合矮生常绿乔木与灌木类群，这类类群主要分布于地中海灌丛及相关半干旱生境中。