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...研究背景：爱德华兹（Edwards）等人于近期发表在《美国植物学杂志（American Journal of Botany，缩写为Am. J. Bot.）》第103卷第975至978页的一篇评论文章提出，幼叶在芽苞内的排布约束可解释非全缘叶缘与纬度之间的正相关关系，但该研究未全面考量其他潜在解释路径。 研究方法：本文梳理了关于叶缘齿状特征功能意义的六大主流假说的逻辑与实证依据，各假说分别涉及：(1) 叶片降温效应；(2) 主脉对所支配区域的最优支撑与养分供给；(3) 叶缘光合效能提升；(4) 排水器功能；(5) 植食动物防御；(6) 芽苞排布适配。 主要结果：除支撑-供给假说外，其余所有假说均被理论与实证研究证伪；该假说预示薄型叶片更易呈现非全缘叶缘。针对被子植物、埃尔云克植物区系以及荚蒾属（Viburnum）类群开展的系统发育结构化分析均证实，非全缘叶缘的出现频率确实更高……