COLLABORATIVE RESEARCH: Testing a new hypothesis for global patterns in leaf form using Viburnum (Adoxaceae)

长期以来，科学家们已经发现了热带和温带气候之间的叶子形状的全球模式：热带叶子的边缘光滑，而生活在寒冷地区的植物的叶子有牙齿或裂片，就像桦树或枫树一样。这种关系是如此强烈，以至于古植物学家使用化石植物群中的叶子形状作为温度的替代品，从而能够估计随着时间的推移的气候变化。但对于这种关系为什么会存在，仍然没有机械性的理解。PI假设，温带植物复杂叶缘的进化部分是由于年轻的未成熟叶片被塞进越冬芽的方式造成的。这是受到最近芽中有效折叠叶片的数学模型的启发，以及对植物内部叶片形态差异的观察。Viburnum是约170种木本灌木和乔木的谱系，在过去的5000万年里，这些灌木和乔木在热带和温带森林之间多次迁徙，并表现出预期的树叶形状变化。PI将记录生长时间、叶片寿命和芽内叶片堆积的模式，并收集一组跨越热带-温带梯度的Viburnum物种的一套相关形态和生理特征的额外数据。他们还将继续对一个普通花园中的约30种Viburnum物种进行长期物候监测。这是一个高度合作和跨学科的项目，包括来自其他四个国家的生物学家和一名应用数学家。PI还将开发为小学生设计的教育模块，旨在弥合数学和生物之间的差距，使用折纸和基本几何原理来理解常见的树叶形状。

Scientists have long recognized a global pattern in leaf shape between tropical and temperate climates: tropical leaves have smooth margins while plants living in cold regions have leaves with teeth or lobes, like a birch or a maple. The relationship is so strong that paleobotanists use leaf shapes in fossil floras as a proxy for temperature, allowing for estimates of climate change through time. But there is still no mechanistic understanding of why this relationship exists. The PIs hypothesize that the evolution of complex leaf margins in temperate plants results in part from the way that young, immature leaves are packed into overwintering buds. This is inspired by recent mathematical models of efficient leaf folding within buds, and by observations of within-plant differences in leaf form. Viburnum is a lineage of ~170 species of woody shrubs and trees that have shifted between tropical and temperate forests many times throughout the past 50 million years, and exhibit the expected changes in leaf shape. The PIs will document timing of growth, leaf lifespan, and patterns of leaf-packing within buds, and gather additional data on a suite of relevant morphological and physiological traits on a set of Viburnum species spanning the tropical-temperate gradient. They will also continue long-term phenological monitoring of ~30 Viburnum species in a common garden. This is a highly collaborative and interdisciplinary project, involving biologists from four other nations as well as an applied mathematician. The PIs will also develop educational modules designed for elementary school children aimed to bridge the gap between math and biology, using origami and basic geometric principles to understand common leaf shapes.