New highlights of phytolith structure and occluded carbon location: 3-D X-ray microscopy and NanoSIMS results
New highlights of phytolith structure and occluded carbon location: 3-D X-ray microscopy and NanoSIMS results
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DOI：
10.5194/bg-12-863-2015
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发表时间：
2015-01-01
期刊：
影响因子：
4.9
通讯作者：
Santos, G. M.
中科院分区：
文献类型：
--
作者：
Alexandre, A.;Basile-Doelsch, I.;Santos, G. M.
植物岩含有被称为phytC的封闭有机化合物。近年来，全球碳循环中植物碳的含量、性质、来源、古环境意义及其影响日益成为人们争论的话题。由于缺乏植物岩中植物tc的原位表征，导致了不一致性。本文利用三维x射线显微技术，在高空间分辨率下重建了收获草短细胞（GSC）植岩的三维结构。虽然该技术已广泛用于生物系统的三维重建，但从未在高分辨率模式下应用于二氧化硅颗粒。同时，我们利用纳米二级离子质谱（NanoSIMS）研究了phytC的位置。我们的数据证明了二氧化硅结构包含微米级的内腔。这些内腔有时被观察到与外界隔绝。它们的开口可能是原始特征，也可能是化学萃取过程中二氧化硅开始溶解的结果，模仿自然环境中可能发生的逐渐溶解过程。因此，原本可能占据空腔的植物易受快速氧化的影响。NanoSIMS技术没有检测到它。然而，我们发现了另一种持续分布在二氧化硅结构中并受其保护的植物碳池。其N / C比值（0.27）与氨基酸的存在一致。这些发现为进一步表征phytC的起源、遮挡过程、性质和可及性奠定了基础，并为评估其在全球C循环中的意义奠定了前提。
Phytoliths contain occluded organic compounds called phytC. Recently, phytC content, nature, origin, paleoenvironmental meaning and impact in the global C cycle have been the subject of increasing debate. Inconsistencies were fed by the scarcity of in situ characterizations of phytC in phytoliths. Here we reconstructed at high spatial resolution the 3-D structure of harvested grass short cell (GSC) phytoliths using 3-D X-ray microscopy. While this technique has been widely used for 3-D reconstruction of biological systems it has never been applied in high-resolution mode to silica particles. Simultaneously, we investigated the location of phytC using nanoscale secondary ion mass spectrometry (NanoSIMS). Our data evidenced that the silica structure contains micrometric internal cavities. These internal cavities were sometimes observed isolated from the outside. Their opening may be an original feature or may result from a beginning of dissolution of silica during the chemical extraction procedure, mimicking the progressive dissolution process that can happen in natural environments. The phytC that may originally occupy the cavities is thus susceptible to rapid oxidation. It was not detected by the NanoSIMS technique. However, another pool of phytC, continuously distributed in and protected by the silica structure, was observed. Its N / C ratio (0.27) is in agreement with the presence of amino acids. These findings constitute a basis to further characterize the origin, occlusion process, nature and accessibility of phytC, as a prerequisite for assessing its significance in the global C cycle.