Shedding synchrotron light on the fossil record of early plant evolution

陆地植物的进化改变了我们星球的表面、大气和海洋--通过生物合成和增加风化速率来固定碳，以及通过建立适合动物居住的陆地环境。我们对这一过程的理解并不依赖于原始的活植物（苔藓、地钱和金鱼藻），它们的进化关系还不清楚，而是来自最早植物的微观化石遗迹。两种石化机制为我们提供了独特的见解：（i）晚泥盆世Rhynie Chert中热喷口群落的快照，其中邻近的植物被包裹并保存在来自热流体的矿物中，以及（ii）在志留纪和泥盆纪的许多更古老的沉积物中，野火对植物的木炭化作用。木炭化的过程是瞬间的石化-它使植物材料化学惰性和物理脆性，但抵抗细菌腐烂，并保留细胞水平的解剖结构-使以这种方式保存的化石成为植物进化史上无与伦比的档案。原始陆地植物的古代木炭化遗骸在细胞水平上对它们的解剖结构有着深刻的了解，但要解开这些信息是非常困难的。这种宝贵的材料传统上是通过破坏性解剖来研究的，沿着沿着随机方向打开的裂缝，可以瞥见内部解剖结构。整体解剖结构必须通过破坏许多标本来拼凑，内部结构之间的联系是推断性的;许多结构根本无法揭示。明显的替代方法是使用非侵入性计算机断层扫描- CT扫描。我们在2007年引入了一种非常高分辨率的方法，使用同步加速器（一种粒子加速器）研究高级种子和开花植物的炭化遗骸。然而，对最古老的陆地植物遗骸的分析结果是可怕的-黄铁矿（傻瓜金）的晶体已经在化石遗骸的细胞空间内生长，黄铁矿（高吸收和散射）和木炭（极低吸收）之间的巨大差异X射线吸收使得不可能做出任何解剖结构。自2007年以来，同步加速器光束线测量技术以及它收集的数据处理都有了改进。特别是，将原始测量值转换为X射线切片的阶段，已经通过滤波算法进行了改进，使我们能够看到化石的解剖细节。我们的项目将需要优化测量参数和数据处理阶段涉及的算法，通过与我们长期的项目合作伙伴Marco Stampanoni教授在瑞士光源同步加速器的合作-他们建造仪器并编程数据处理算法。我们将利用这些先进的CT扫描新材料的早期植物遗骸，我们将恢复从关键的化石存款在什罗普郡。我们有丰富的经验，从同步加速器数据化石的计算机建模，我们将分析化石的计算机模型，解剖他们几乎更好地了解这些早期植物的解剖和生理，在密切合作与世界专家在这些生物体的生物学，教授戴安娜爱德华兹FRS。这项工作将使我们能够了解早期陆地植物进化的进化步骤顺序，反过来，这项工作将有助于我们了解陆地植物如何改变地球，也可能在解决有关其生活亲属进化关系的争议方面发挥关键作用。

The evolution of land plants transformed the surface, atmosphere and ocean of our planet - by fixing carbon through biosynthesis and increased rates of weathering, as well as through establishing a terrestrial environment habitable by animals. Our understanding of how this was brought about rests less on primitive living plants (mosses, liverworts and hornworts) whose evolutionary relationships are poorly understood but, rather, from the microscopic fossil remains of the earliest plants. Two fossilization mechanisms have provided us with unique insights: (i) the snapshot of a hot vent community in the Late Devonian Rhynie Chert where the neighboring plants were enveloped and preserved in minerals from the hot fluids, and (ii) the charcoalification of plants by wildfires in a number of much older deposits through the Silurian and Devonian. The process of charcoalification is instant fossilization - it makes plant material chemically inert and physically brittle but resistant to bacterial decay and preserves anatomical structure to the cellular level - making fossils preserved in this way an unparalleled archive in of plant evolutionary history. Ancient charcolified remains of primitive land plants hold insights into their anatomy to the cellular level, but unlocking this information is very difficult. This invaluable material has traditionally been studied by destructively dissection, yielding glimpses of the internal anatomy along cracks that open up in chance orientations. The overall anatomy has to be pieced together by destroying many specimens and the linkage between internal structures are inferential; many structures are never revealed at all. The obvious alternative is to use non-invasive computed tomography - CT scanning. We introduced a very high resolution method in 2007 of studying charcolified remains of advanced seed and flowering plants using a synchrotron - a kind of particle accelerator. However, the results of analyses of the most ancient land plant remains were terrible - crystals of pyrite (fools gold) have grown within the cell spaces of the fossil remains and the huge difference x-ray absorption between the pyrite (high absorption and scattering) and the charcoal (extremely low absorption) making it impossible to make out any anatomical structure. Since 2007 there have been improvements in the synchrotron beamline measurement technology, but also in the processing of the data that it collects. In particular, the stage in which the raw measurements are converted to x-ray slices, has been improved with filtering algorithms that allow us to see the anatomy of the fossil in pin-sharp detail. Our project will entail optimising the measurement parameters and of algorithms involved in the data processing stages, through collaboration with our long-standing Project Partner Prof Marco Stampanoni at the Swiss Light Source Synchrotron - who build the instruments and program the algorithms for data processing. We will exploit these advances in CT scanning new material of early plant remains that we will recover from the critical fossil deposit in Shropshire. We have extensive experience of computer modelling of fossils from synchrotron data and we will analyse computer models of the fossils, dissecting them virtually to better understand the anatomy and physiology of these early plants, in intimate collaboration with the world expert in the biology of these organisms, Prof Dianne Edwards FRS. This work will allow us to understand the sequence of evolutionary steps in early land plant evolution and, in turn, this work will contribute to our understanding of how land plants transformed the planet, and may also prove pivotal in resolving controversy concerning the evolutionary relationships of their living relatives.