Three keys to the radiation of angiosperms into freezing environments
Three keys to the radiation of angiosperms into freezing environments
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DOI：
10.1038/nature12872
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发表时间：
2014-02-06
期刊：
影响因子：
64.8
通讯作者：
Beaulieu, Jeremy M.
中科院分区：
文献类型：
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作者：
Zanne, Amy E.;Tank, David C.;Beaulieu, Jeremy M.
早期开花植物被认为是仅限于温暖栖息地的木本物种（1-3）。这一谱系几乎辐射到每一种气候中，具有多种生长形式（4）。随着被子植物的扩散和气候的变化，它们进化出了科普间歇性冰冻的机制。为了探索支撑在冷冻条件下持续能力的性状的进化，我们组装了一个大型物种水平的生长习性数据库（木本或草本; 49，064种），以及叶物候学（万年青或落叶），水力导管直径（即木质部导管和管胞）和气候占领（暴露于冷冻）。为了模拟物种特征和气候变化的演变，我们将这些数据与陆地植物的无与伦比的分子遗传学（32，223种）相结合。在这里，我们表明，木本分支成功地移动到易结冰的环境中，要么拥有运输网络的小安全管道（5）和/或关闭液压功能下降叶片在冻结期间。草本植物通过廉价的地上组织衰老来避免冰冻期。长期以来，生长习性一直被认为是不稳定的（6），但我们发现生长习性比气候占用更不稳定。此外，冰冻环境中大部分都是已经成为草本植物的谱系，或者在保持木质时已经有了小管道（即在气候占领之前进化的特征）。相比之下，大多数落叶木本谱系有一个进化的转变，季节性脱落的叶子后，才暴露于冻结（即气候占用演变之前的特点）。被子植物居住在新的寒冷环境中，他们必须获得新的结构和功能性状的解决方案，我们的研究结果表明，这些解决方案中的许多可能是收购前进入寒冷。
Early flowering plants are thought to have been woody species restricted to warm habitats(1-3). This lineage has since radiated into almost every climate, with manifold growth forms(4). As angiosperms spread and climate changed, they evolved mechanisms to cope with episodic freezing. To explore the evolution of traits underpinning the ability to persist in freezing conditions, we assembled a large species-level database of growth habit (woody or herbaceous; 49,064 species), as well as leaf phenology (evergreen or deciduous), diameter of hydraulic conduits (that is, xylem vessels and tracheids) and climate occupancies (exposure to freezing). To model the evolution of species' traits and climate occupancies, we combined these data with an unparalleled dated molecular phylogeny (32,223 species) for land plants. Here we show that woody clades successfully moved into freezing-prone environments by either possessing transport networks of small safe conduits(5) and/or shutting down hydraulic function by dropping leaves during freezing. Herbaceous species largely avoided freezing periods by senescing cheaply constructed aboveground tissue. Growth habit has long been considered labile(6), but we find that growth habit was less labile than climate occupancy. Additionally, freezing environments were largely filled by lineages that had already become herbs or, when remaining woody, already had small conduits (that is, the trait evolved before the climate occupancy). By contrast, most deciduous woody lineages had an evolutionary shift to seasonally shedding their leaves only after exposure to freezing (that is, the climate occupancy evolved before the trait). For angiosperms to inhabit novel cold environments they had to gain new structural and functional trait solutions; our results suggest that many of these solutions were probably acquired before their foray into the cold.