Rhizoliths, that is, roots fossilized by secondary carbonates, have been known for ages and are increasingly used for paleoenvironmental reconstructions. However, knowledge about their formation mechanisms remains limited. This study reports the mineralogical and chemical characterization of rhizoliths at different stages of mineralization and fossilization in the Late Pleistocene loess–paleosol sequence of Nussloch (SW Germany). Scanning electron microscopy coupled with elemental mapping and ¹³C solid‐state nuclear magnetic resonance were used to concomitantly characterize the mineral and organic matter of the rhizoliths. These joint analyses showed for the first time that large rhizoliths are not necessarily remains of single large roots but consist of numerous microrhizoliths as remains of fine roots, formed mainly by calcium carbonates with only low amounts of Mg and Si. They further revealed that the precipitation of secondary carbonates occurs not only around, but also within the plant root and that fossilization leads to the selective preservation of recalcitrant root biopolymers—lignin and suberin. The precipitation of secondary carbonates was observed to occur first around fine roots, the epidermis acting as a first barrier, and then within the root, within the cortex cells, and even sometimes around the phloem and within the xylem. This study suggests that the calcification of plant roots starts during the lifetime of the plant and continues after its death. This has to be systematically investigated to understand the stratigraphic context before using (micro)rhizoliths for paleoenvironmental reconstructions in terrestrial sediments.

中文翻译：

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化学和微观形态学分析破译了植物根钙化的多个阶段。

根际石，即由次生碳酸盐化石的根，已经有很长的历史了，并越来越多地用于古环境的重建。但是，关于其形成机理的知识仍然有限。这项研究报告了Nussloch晚更新世黄土-古土壤序列中成矿和化石作用不同阶段的根茎的矿物学和化学特征（德国德国）。扫描电子显微镜结合元素图谱和¹³C固态核磁共振被用来表征根茎的矿物和有机质。这些联合分析首次表明，大根茎不一定是单个大根的残留物，而是由许多细根的微根石组成，主要由仅含少量Mg和Si的碳酸钙形成。他们进一步揭示，次生碳酸盐的沉淀不仅发生在植物根部附近，而且还发生在植物根部，而化石作用导致选择性顽固的根部生物聚合物木质素和木栓质的保存。观察到次生碳酸盐的沉淀首先在细根周围发生，表皮作为第一屏障，然后在根内，皮质细胞内沉淀，甚至有时在韧皮部周围和木质部内部。这项研究表明，植物根的钙化在植物的生命周期内开始，并在其死亡后继续。在使用（微）根瘤石进行陆相沉积物中的古环境重建之前，必须对此进行系统地研究，以了解地层背景。