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、大气层和海洋--通过生物合成和增加风化速率固定碳，以及通过建立一个适合动物居住的陆地环境。我们对这一现象如何产生的理解，较少依赖于原始的活植物(苔藓、地钱和角藻)，它们的进化关系鲜为人知，而是来自最早的植物的微观化石遗骸。两种化石机制为我们提供了独特的见解：(I)晚泥盆世Rhynie Chert中的热喷口群落的快照，其中邻近的植物被热流体的矿物包裹并保存，以及(Ii)在志留纪和泥盆纪的一些更古老的沉积物中，野火对植物的木炭化作用。木炭化的过程是瞬间的石化-它使植物材料在化学上惰性和物理上易碎，但耐细菌腐烂，并保留了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。古代原始陆地植物的炭化遗骸将对它们的解剖学的洞察保持到细胞水平，但解开这些信息是非常困难的。这种无价的材料传统上是通过破坏性解剖来研究的，可以一瞥沿着偶然方向打开的裂缝的内部解剖结构。整个解剖结构必须通过销毁许多标本来拼凑起来，内部结构之间的联系是推论的；许多结构根本就没有揭示出来。显而易见的替代方案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残留物。然而，对最古老的陆地植物遗骸的分析结果很可怕--在化石遗骸的细胞空间中生长了黄铁矿(愚蠢的金)晶体，黄铁矿(高吸收和散射)和木炭(极低吸收)之间的X射线吸收差异巨大，使得无法分辨出任何解剖结构。自2007年以来，同步加速器光束线测量技术有了改进，它收集的数据的处理也有了改进。特别是，将原始测量数据转换为X射线切片的阶段，已经通过过滤算法得到了改进，使我们能够看到化石的精确细节。我们的项目将需要通过与瑞士光源同步加速器的长期项目合作伙伴Marco Stampanoni教授合作，优化数据处理阶段涉及的测量参数和算法-谁制造仪器并为数据处理算法编程。我们将在CT扫描方面利用这些进展，从什罗普郡的关键化石沉积物中提取早期植物遗骸的新材料。我们在根据同步加速器数据对化石进行计算机建模方面拥有丰富的经验，我们将与世界生物生物学专家Dianne Edwards FRS教授密切合作，分析化石的计算机模型，虚拟解剖它们，以更好地了解这些早期植物的解剖学和生理学。这项工作将使我们能够理解早期陆地植物进化的顺序，反过来，这项工作将有助于我们理解陆地植物是如何改变地球的，也可能被证明在解决关于它们现存亲属进化关系的争议方面起到关键作用。

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.