Modern cryptogamic ground covers (CGCs), comprising assemblages of bryophytes (hornworts, liverworts, mosses), fungi, bacteria, lichens and algae, are thought to resemble early divergent terrestrial communities. However, limited in situ plant and other fossils in the rock record, and a lack of CGC‐like soils reported in the pre‐Silurian sedimentological record, have hindered understanding of the structure, composition and interactions within the earliest CGCs. A key question is how the earliest CGC‐like organisms drove weathering on primordial terrestrial surfaces (regolith), leading to the early stages of soil development as proto‐soils, and subsequently contributing to large‐scale biogeochemical shifts in the Earth System. Here, we employed a novel qualitative, quantitative and multi‐dimensional imaging approach through X‐ray micro‐computed tomography, scanning electron, and optical microscopy to investigate whether different combinations of modern CGC organisms from primordial‐like settings in Iceland develop organism‐specific soil forming features at the macro‐ and micro‐scales. Additionally, we analysed CGCs growing on hard rocky substrates to investigate the initiation of weathering processes non‐destructively in 3D. We show that thalloid CGC organisms (liverworts, hornworts) develop thin organic layers at the surface (<1 cm) with limited subsurface structural development, whereas leafy mosses and communities of mixed organisms form profiles that are thicker (up to ~ 7 cm), structurally more complex, and more organic‐rich. We term these thin layers and profiles proto‐soils. Component analyses from X‐ray micro‐computed tomography data show that thickness and structure of these proto‐soils are determined by the type of colonising organism(s), suggesting that the evolution of more complex soils through the Palaeozoic may have been driven by a shift in body plan of CGC‐like organisms from flattened and appressed to upright and leafy. Our results provide a framework for identifying CGC‐like proto‐soils in the rock record and a new proxy for understanding organism–soil interactions in ancient terrestrial biospheres and their contribution to the early stages of soil formation.

中文翻译：

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地下地面覆盖物作为早期陆地生物圈的类似物：生物介导的原生土壤的起始和进化

现代苔藓地被植物（CGC），包括苔藓植物（金缕梅，地草，苔藓），真菌，细菌，地衣和藻类的组合，类似于早期散布的陆地群落。但是，岩石记录中的原位植物和其他化石数量有限，Silurian以前的沉积学记录中缺乏CGC类土壤，这阻碍了人们对最早的CGC内部结构，组成和相互作用的理解。一个关键问题是最早的类CGC微生物如何在原始陆相表面（风化层）上推动风化，导致土壤发展为原生土壤的早期阶段，并随后导致地球系统中的大规模生物地球化学变化。在这里，我们采用了一种新颖的定性 通过X射线计算机断层扫描，扫描电子和光学显微镜进行定量和多维成像的方法，以调查冰岛原始环境中现代CGC生物的不同组合是否在宏观和宏观上形成了特定于生物的土壤形成特征微型秤。此外，我们分析了在坚硬岩石基底上生长的CGC，以无损方式研究了3D中风化过程的开始。我们显示，藻类CGC生物（柳蒿，金缕梅）在表面（<1厘米）处发育出薄薄的有机层，且地下结构发育受到限制，而绿叶苔藓和混合生物群落形成的剖面更厚（约7厘米），结构上更复杂，有机更丰富。我们称这些薄层和剖面为原土。X射线微计算机断层扫描数据的成分分析表明，这些原始土壤的厚度和结构由定殖生物的类型决定，这表明通过古生代的更复杂土壤的演化可能是由土壤微生物驱动的。 CGC样生物的身体计划从扁平化和贴紧转移到直立和多叶。我们的结果提供了一个框架，可用于识别岩石记录中的类似CGC的原始土壤，并为理解古代陆地生物圈中生物与土壤之间的相互作用及其对土壤早期形成的贡献提供了新的代理。这表明，通过古生代的更复杂土壤的演化可能是由于CGC类生物体的身体计划从扁平化和贴紧型变为直立和多叶的。我们的结果提供了一个框架，可用于识别岩石记录中的类似CGC的原始土壤，并为理解古代陆地生物圈中生物与土壤之间的相互作用及其对土壤早期形成的贡献提供了新的代理。这表明，通过古生代的更复杂土壤的演化可能是由于CGC类生物体的身体计划从扁平化和贴紧型变为直立和多叶的。我们的结果提供了一个框架，可用于识别岩石记录中的类似CGC的原始土壤，并为理解古代陆地生物圈中生物与土壤之间的相互作用及其对土壤早期形成的贡献提供了新的代理。