Developmental and biophysical determinants of grass leaf size worldwide

One of the most notable ecological trends-described more than 2,300 years ago by Theophrastus-is the association of small leaves with dry and cold climates, which has recently been recognized for eudicotyledonous plants at a global scale(1-3). For eudicotyledons, this pattern has been attributed to the fact that small leaves have a thinner boundary layer that helps to avoid extreme leaf temperatures(4) and their leaf development results in vein traits that improve water transport under cold or dry climates(5,6). However, the global distribution of leaf size and its adaptive basis have not been tested in the grasses, which represent a diverse lineage that is distinct in leaf morphology and that contributes 33% of terrestrial primary productivity (including the bulk of crop production)(7). Here we demonstrate that grasses have shorter and narrower leaves under colder and drier climates worldwide. We show that small grass leaves have thermal advantages and vein development that contrast with those of eudicotyledons, but that also explain the abundance of small leaves in cold and dry climates. The worldwide distribution of leaf size in grasses exemplifies how biophysical and developmental processes result in convergence across major lineages in adaptation to climate globally, and highlights the importance of leaf size and venation architecture for grass performance in past, present and future ecosystems.

最显著的生态趋势之一——2300多年前由泰奥弗拉斯托斯所描述——是小叶与干燥和寒冷气候的关联，这一关联最近在全球范围内在真双子叶植物中得到了确认（1 - 3）。对于真双子叶植物，这种模式归因于小叶具有更薄的边界层，有助于避免极端的叶片温度（4），并且它们的叶片发育形成的叶脉特征可改善在寒冷或干燥气候下的水分运输（5,6）。然而，叶片大小的全球分布及其适应性基础尚未在禾本科植物中得到验证，禾本科植物代表了一个多样的谱系，在叶片形态上有独特之处，并且贡献了陆地初级生产力的33%（包括大部分农作物产量）（7）。在此我们证明，在全球更寒冷和更干燥的气候条件下，禾本科植物具有更短且更窄的叶片。我们表明，禾本科植物的小叶具有热学优势以及与真双子叶植物不同的叶脉发育，但这也解释了在寒冷和干燥气候下小叶的大量存在。禾本科植物叶片大小的全球分布例证了生物物理和发育过程如何导致主要谱系在全球适应气候方面的趋同，并凸显了叶片大小和叶脉结构对于禾本科植物在过去、现在和未来生态系统中表现的重要性。