Phylogenetic analyses reveal the shady history of C4 grasses
Phylogenetic analyses reveal the shady history of C4 grasses
复制标题
DOI：
10.1073/pnas.0909672107
复制
发表时间：
2010-02-09
影响因子：
11.1
通讯作者：
Smith, Stephen A.
中科院分区：
文献类型：
--
作者：
Edwards, Erika J.;Smith, Stephen A.
草原覆盖了地球陆地表面的20%以上，它们的崛起是地球历史上生物群落进化中最引人注目的事件之一。草具有两个主要的光合作用途径：C-3途径，这是典型的大多数植物和一个专门的C-4途径，最大限度地减少光呼吸，从而提高光合性能在高温和/或低CO2环境。C-4禾本科植物主要分布在热带和亚热带草原和稀树草原，C-3禾本科植物主要分布在世界上较冷的温带草原地区。这一惊人的模式被归因于C-4生理学，暗示着该途径的进化使C-4草能够在比它们的C-3亲戚更温暖的气候中持续存在。我们结合了来自两个公共档案馆的地理空间和分子序列数据，从110多万份植物标本中提取了1,230个分类群的草类，以及所有物种的气候数据。在这里，我们表明，草类是祖先的一个温暖的适应分支，C-4进化与温带和热带生物群落之间的变化是不相关的。相反，18 20推断C-4的起源与平均年降水量显着减少。这些变化与热带森林环境向热带林地/稀树草原系统的转移是一致的。我们的结论是，C-4进化的草在很大程度上与迁移出林下植被，并进入开放的冠层环境。此外，我们认为，在某些C-3谱系的耐寒性的演变是一个被忽视的创新，深刻地影响了整个地球仪草原群落的格局。
Grasslands cover more than 20% of the Earth's terrestrial surface, and their rise to dominance is one of the most dramatic events of biome evolution in Earth history. Grasses possess two main photosynthetic pathways: the C-3 pathway that is typical of most plants and a specialized C-4 pathway that minimizes photorespiration and thus increases photosynthetic performance in high-temperature and/or low-CO2 environments. C-4 grasses dominate tropical and subtropical grasslands and savannas, and C-3 grasses dominate the world's cooler temperate grassland regions. This striking pattern has been attributed to C-4 physiology, with the implication that the evolution of the pathway enabled C-4 grasses to persist in warmer climates than their C-3 relatives. We combined geospatial and molecular sequence data from two public archives to produce a 1,230-taxon phylogeny of the grasses with accompanying climate data for all species, extracted from more than 1.1 million herbarium specimens. Here we show that grasses are ancestrally a warm-adapted clade and that C-4 evolution was not correlated with shifts between temperate and tropical biomes. Instead, 18 of 20 inferred C-4 origins were correlated with marked reductions in mean annual precipitation. These changes are consistent with a shift out of tropical forest environments and into tropical woodland/savanna systems. We conclude that C-4 evolution in grasses coincided largely with migration out of the understory and into open-canopy environments. Furthermore, we argue that the evolution of cold tolerance in certain C-3 lineages is an overlooked innovation that has profoundly influenced the patterning of grassland communities across the globe.