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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Phylogenetic analyses reveal the shady history of C_4 grasses
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Phylogenetic analyses reveal the shady history of C_4 grasses

机译：系统发育分析揭示了C_4草的阴暗历史

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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 photo-synthetic 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-CO_2 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.
机译：草原占地球陆地表面的20％以上，它们的优势地位是地球历史上生物群落进化最剧烈的事件之一。草具有两个主要的光合作用途径：大多数植物中常见的C_3途径和专门的C_4途径，该途径可最大程度地减少光呼吸作用，从而提高高温和/或低CO_2环境下的光合作用。 C_4草在热带和亚热带草原和热带稀树草原中占主导地位，C_3草在世界上较凉爽的温带草原地区中占主导地位。这种引人注目的模式归因于C_4生理，这意味着该途径的演变使C_4草比其C_3近缘种能够在更温暖的气候下生存。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，得出了1,230个分类的草类系统发育，以及从超过110万个标本室标本中提取的所有物种的伴随气候数据。在这里，我们表明草在祖先是一个适应温暖的进化枝，C_4的进化与温带和热带生物群落之间的变化无关。相反，在20个推断的C_4起源中，有18个与平均年降水量明显减少有关。这些变化与从热带森林环境向热带林地/热​​带稀树草原系统的转移相一致。我们得出的结论是，草丛中的C_4进化与从林下迁移到开放冠层环境中的迁移相吻合。此外，我们认为某些C_3世系的耐寒性进化是一项被忽视的创新，深刻影响了全球草地群落的格局。

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