Towards producing pure phytolith concentrates from plants that are suitable for carbon isotopic analysis
Towards producing pure phytolith concentrates from plants that are suitable for carbon isotopic analysis
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DOI：
10.1016/j.revpalbo.2013.06.001
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发表时间：
2013-10-15
影响因子：
1.9
通讯作者：
Santos, Guaciara M.
中科院分区：
文献类型：
--
作者：
Corbineau, Remi;Reyerson, Paul E.;Santos, Guaciara M.
植硅石是在植物的整个生命过程中在高等植物组织的细胞内部或细胞之间形成的无定形二氧化硅的微米颗粒。从沉积物和埋藏土壤中提取的植硅体形态组合越来越多地用作草地多样性和树木覆盖密度的代理。当在考古遗址中发现大量时，它们可用于确定饮食习惯，文化和农业实践。植硅体可以包含少量的C在其结构中被封闭（phytC）。一般认为，这种植物碳的来源是大气中的CO2，是由植物通过光合作用固定的。因此，植硅体（δ C-13，C-14）的同位素分析，预计将分别告知光合途径或矿化寄主植物的年龄。然而，最近对从土壤和收获的草中提取的植硅体浓缩物中的植硅体C进行的C-14分析得出了数百至数千年的出乎意料的C-14年龄。这些C-14 phytC的结果提出了一个可能的来源的难处理/老土壤有机质组分的问题，由根，这可以附着或封闭在植硅体。同时，这些结果强调了需要制定标准化的协议，导致浓缩完全没有有机残留物，以及一个强大的方法来检查植硅石纯度。因此，这项工作的目标是开发从植物中提取植硅体的协议，导致100%的植硅体纯度，如phytC分析所需。方案1利用干灰化和酸消化的多步骤过程，而方案2也使用酸消化以及去除表面层的单独的碱浸渍步骤。通过使用SEM-EDS分析，以半定量的方式测量植硅石浓缩物的纯度。植硅体纯度的质量检查可以揭示植硅体浓缩物中的小C颗粒污染，这可能会使植硅体C的同位素和定量分析产生相当大的偏差。结果表明，这两种方案能够完全去除小碳颗粒污染。方案1生产的植硅石浓缩物具有良好定义的形态，适合于形态和同位素分析。然而，碳产率的测量表明，方案1可能诱导碳泄漏，导致较低的回收率。方案2更快，导致更高的C产率，但可能导致溶解开始。有了这些方案，可以适当地调查phytC的来源。(C)2013爱思唯尔有限公司版权所有。
Phytoliths are micrometric particles of amorphous silica that form inside or between the cells of higher plant tissues throughout the life of a plant. Phytolith morphological assemblages extracted from sediments and buried soils are increasingly used as proxies of grassland diversity and tree cover density. When found in significant amounts in archeological sites they can be used for identifying food habits, cultural and agricultural practices. Phytoliths can contain small amounts of C occluded in their structure (phytC). It is generally assumed that the source of this phytC is atmospheric CO2 that was fixed by the plant via photosynthesis. Isotopic analyses of phytoliths (delta C-13, C-14) were thus expected to inform respectively on the photosynthetic pathway or on the age of the mineralized host plants. However recent C-14 analyses of phytC from phytolith concentrates extracted from soils and harvested grasses yielded unexpected C-14 ages of several hundreds to kyr old. These C-14 phytC results raised the question of a possible source of refractory/old soil organic matter component taken up by roots, which can be attached or occluded in phytoliths. Simultaneously these results highlighted the need for setting standardized protocols leading to concentrates entirely devoid of organic residues, as well as for a robust method for checking phytolith purity. The goal of this work was thus to develop protocols for extracting phytoliths from plants, leading to 100% phytolith purity, as required for phytC analyses. Protocol 1 utilizes a multi-step process of dry ashing and acid digestion, while protocol 2 also uses acid digestion as well as a separate alkali immersion step which removes surface layers. Phytolith concentrate purity was gauged in a semi-quantitative fashion through the use of SEM-EDS analysis. This quality check for phytolith purity can reveal small C particulate contamination of phytolith concentrates that may considerably bias isotopic and quantitative analyses of phytC. Results indicate that the two protocols were able to entirely remove small C particulate contamination. Protocol 1 produced phytolith concentrates with well defined morphologies suitable for both morphological and isotopic analyses. However measurement of C yields showed that protocol 1 probably induced C leakage, leading to lower recovery. Protocol 2 is faster, leads to higher C yield but may lead to a beginning of dissolution. With these protocols on hand, sources of phytC can be properly investigated. (C) 2013 Elsevier B.V. All rights reserved.