Evolution of leaf-form in land plants linked to atmospheric CO2 decline in the Late Palaeozoic era
Evolution of leaf-form in land plants linked to atmospheric CO2 decline in the Late Palaeozoic era
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DOI：
10.1038/35066546
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发表时间：
2001-03-15
期刊：
影响因子：
64.8
通讯作者：
Chaloner, WG
中科院分区：
文献类型：
--
作者：
Beerling, DJ;Osborne, CP;Chaloner, WG
直到大约3.6亿年前的泥盆纪末期，才出现了大叶植物的叶子，以及它们的分支脉和扁平状。这发生在简单的无叶维管植物在晚志留世/早泥盆世（1，2）首次殖民于陆地之后约4000万年，但现代植物这种共同特征缓慢出现的原因目前尚未解决。在这里，我们使用化石叶特征和生物物理学原理进行了一系列定量分析，结果表明，延迟与晚古生代大气pCO（2）下降90%有因果关系（3，4）。与典型的早泥盆世陆地植物的模拟相反，无叶茎上的气孔很少（5），具有相同气孔特征的扁平叶的模拟表明，由于更多的太阳能拦截和低蒸腾作用，它会遭受致命的过热。当扁平叶首次出现在晚泥盆世，随后在石炭纪时期多样化时，它们具有显著较高的气孔密度（6）。这一观察结果与pCO（2）对气孔发育的影响一致（7），并表明扁平叶的进化只能在气孔密度增加后发生，从而允许足以维持凉爽和有活力的叶温的较高蒸腾速率。
The widespread appearance of megaphyll leaves, with their branched veins and planate form, did not occur until the close of the Devonian period at about 360 Myr ago. This happened about 40 Myr after simple leafless vascular plants first colonized the land in the Late Silurian/Early Devonian(1,2), but the reason for the slow emergence of this common feature of present-day plants is presently unresolved. Here we show, in a series of quantitative analyses using fossil leaf characters and biophysical principles, that the delay was causally linked with a 90% drop in atmospheric pCO(2) during the Late Palaeozoic era(3,4). In contrast to simulations for a typical Early Devonian land plant, possessing few stomata(5) on leafless stems, those for a planate leaf with the same stomatal characteristics indicate that it would have suffered lethal overheating, because of greater interception of solar energy and low transpiration. When planate leaves first appeared in the Late Devonian and subsequently diversified in the Carboniferous period, they possessed substantially higher stomatal densities(6). This observation is consistent with the effects of the pCO(2) on stomatal development(7) and suggests that the evolution of planate leaves could only have occurred after an increase in stomatal density, allowing higher transpiration rates that were sufficient to maintain cool and viable leaf temperatures.