Assessing spatial variability of C, Fe and Al concentrations in gleyed soils as a means of understanding the stabilisation of soil organic carbon.

全球土壤储存的碳比大气和植被加起来还要多；这些碳可能以温室气体的形式存在于大气中。维持土壤条件，使其继续储存有机碳是非常重要的；然而，我们对碳如何储存在土壤中的理解是不完整的。据认为，土壤中的某些矿物质，包括铁和铝的氧化物，有助于稳定有机碳，防止微生物攻击，并将其转化为二氧化碳或其他温室气体。然而，目前尚不清楚氧化铁和有机碳究竟是如何相互作用以阻止有机碳被土壤生物代谢的。涝渍土壤在全球约占9亿公顷，是易受永久或暂时涝渍影响的土壤；这就形成了一种独特的模式，即氧化铁在某些区域集中，而在其他区域则不存在。这种氧化铁矿物的空间格局使这些土壤对试图了解有机碳稳定机制的研究人员有用。大量化学分析可以提供有关有机碳、铁和铝的总浓度以及存在的有机物的性质的有价值的信息，但是这些传统的大量化学方法不能提供有关碳和铁氧化物浓度的小尺度空间差异的信息。这种土壤的微观分析将使我们能够直接检查氧化铁和有机碳的浓度，从而有助于阐明土壤中铁氧化物在小距离上稳定有机碳的机制。然而，这些测量的微观尺度使得很难将这些发现推断到整个土壤剖面和更大的土壤体积。拟议的试点项目旨在首次将具体的体积和微观分析技术结合在一起，以研究湿润（涝渍）土壤中有机碳稳定的机制。未受干扰的和散装的样品将从哈伍德森林的土壤，诺森伯兰郡对比排水条件。将对大量样品进行分析，以确定背景土壤条件，碳、铁和铝氧化物的总浓度，以及存在的有机物质的性质。将在土壤上进行一系列越来越激烈的提取，每次提取后回收的溶液将再次进行分析，以确定与不同类型的氧化铁矿物（弱结晶和强结晶）结合的有机碳的性质。未受干扰的土壤块将在树脂中稳定，切片和研磨成薄片，可以使用岩石学和电子显微镜进行检查。可以绘制出氧化铁浓度和损耗的区域，并在厘米、毫米和微米尺度上确定铁、铝、氧和碳的比例。然后，这些部分将受到与大块土壤相同的处理，以去除与先弱后强的结晶氧化铁相关的铁、铝和有机碳。这种新颖的方法将增加我们对碳是如何在倾斜土壤中稳定的理解，以及它对气候变化导致的土壤条件变化有多敏感。这将为土壤碳周转的建模者提供有价值的信息。该项目还将改进研究人员可用的分析方法，这些方法将有助于研究不同土壤中的类似过程；这对于研究农业系统中的碳储存和土壤过程可能特别有用，这对全球温室气体排放做出了重大贡献。

Globally soils store more carbon than the atmosphere and vegetation combined; this carbon could otherwise be present as greenhouse gases in the atmosphere. Maintaining soil conditions such that they continue to store organic carbon is very important; however, our understanding of how carbon is stored in soils is incomplete. It is thought that certain minerals in the soil, including iron and aluminium oxides, help stabilise organic carbon preventing microbial attacking and its conversion to carbon dioxide or other green house gases. However, it is not clear how exactly iron oxides and organic carbon interact to prevent organic carbon being metabolised by soil organisms. Gleyed soils occupy ca. 900 million ha globally, and are soils that are subject to permanent or temporary waterlogging; this results in distinctive patterns whereby iron oxides are concentrated in some areas and are absent from others. This spatial patterning of iron oxide minerals makes these soils useful for researchers trying to understand the mechanisms of organic carbon stabilisation. Bulk chemical analysis can provide valuable information about total concentrations of organic carbon, iron, and aluminium, and about the nature of the organic matter that is present, but these traditional bulk chemical approaches do not provide information about the small scale spatial differences in carbon and iron oxide concentration. Microscopic analysis of such soils would allow us to directly examine the concentration of iron oxides and organic carbon, thus helping to elucidate the mechanisms of organic carbon stabilisation by iron oxides in soil over small distances. However, the microscopic scale of these measurements can make it difficult to extrapolate the findings to whole soil profiles and larger soil volumes. The proposed pilot project aims to bring together for the first time specific bulk and microscopic analytical techniques in order to study the mechanisms of organic carbon stabilisation in gleyed (waterlogged) soils. Undisturbed and bulk samples will be taken from soils at Harwood Forest, Northumberland with contrasting drainage conditions. Bulk samples will be analysed to determine background soil conditions, total concentrations of carbon, iron and aluminium oxides, and the nature of the organic matter present. A sequential series of increasingly aggresive extractions will be carried out on the soils, and the solution recovered after each extraction will be analysed again to determine the nature of the organic carbon bound to different types of iron oxide minerals (weakly crystalline and strongly crystalline). Undisturbed blocks of soil will be stabilised in resin, sliced and lapped to create thin sections which can be examined using petrological and electron microscopes. Areas of iron oxide concentration and depletion can be mapped and the ratio of Fe, Al, O, and C determined across cm, mm and micrometer scales. These sections will then be subjected to the same treatments as the bulk soils in order to remove iron, aluminium and organic carbon associated with first weakly and then strongly crystalline iron oxides. This novel approach will add to our understanding of how carbon is stabilised in gleyed soils and how sensitive it might be to changing soil conditions as a result of climate change. This will provide valuable information for modellers of soil carbon turnover. The project will also refine the analytical methods available to researchers which will be useful for the study of similar processes in different soils; this could be particularly useful for the study of carbon storage and soil processes in agricultural systems, which make a significant contribution to global greenhouse gas emissions.