土壤颜色是反映土壤发生、 形成环境及肥力特征的一项重要物理性状。 通常高有机质含量土壤的颜色比较黑, 但我国典型低有机质含量的砂姜黑土土壤颜色也很黑。 基于传统化学方法的研究认为高度芳构化的腐殖质成分与土粒结合使砂姜黑土呈现黑色。 然而采用化学方法只能提取部分腐殖质成分, 且破坏了有机质及有机无机复合体的化学结构, 其结果不具有代表性。 通过不破坏土壤有机无机复合体结构的物理方法从砂姜黑土中提取黑色物质的研究发现蒙皂石吸附有机质形成的黑色有机无机复合体是砂姜黑土呈现黑色的决定性成分。 但是, 这些黑色有机无机复合体的有机质结构及复合体呈现黑色的机制还不清楚。 本研究旨在通过物理方法从砂姜黑土中提取黑色组分, 从有机质结构及其与蒙皂石矿物作用方面研究这些黑色有机无机复合体的特征, 探讨其呈现黑色的机理。 首先采用物理方法从黄淮海平原三个地点的典型砂姜黑土表土层（0～40 cm）土壤中提取浅色组分［＞53 μm颗粒、 白（W）和浅白(LW)］和黑色组分［浅黑（LB）、 黑（B）和纳米黑（NB）］。 然后采用分光测色仪、 固态13C核磁共振谱仪和X射线衍射仪分别测定不同提取组分的黑度、 有机质结构和蒙皂石含量。 相关分析和通径分析结果表明, 提取组分有机质的羧基碳、 氨基碳、 烷基碳和烷氧碳对砂姜黑土黑度的直接影响效应和间接效应都较大, 芳香碳含量和芳香度对土壤黑度的影响则较小, 蒙皂石对土壤黑度的直接影响效应及其通过羧基碳、 氨基碳和烷基碳对土壤黑度的间接效应都较大。 因此, 砂姜黑土中大量存在的蒙皂石通过吸附有机质中含有生/助色团的羧基碳、 氨基碳、 烷氧碳及烷基碳形成有机-无机复合体是其呈现黑色的主要机制, 并不是传统观点认为的芳香碳及高芳香度。

Soil color is an important physical property for studying the genesis, formation environment and fertility of the soil. Generally, the soil with a higher organic matter content appears darker, but the soil color of the Calci-Aquic (CA) Vertisols with low organic matter contents also appear very black. The results based on the traditional chemical extraction method of black matters indicated that the combination of highly aromatized humus with soil particles makes the CA Vertisols appearing black. However, the chemical extraction method only partially extracted the humus ingredients, and what is more important, it destroyed the structure of organic matter and organic-inorganic complexes. The study on the black matter extracted from the CA Vertisols by the physical extraction method without destroying structures of organic-inorganic complexes showed that the black organic-inorganic complexes formed from smectites adsorbing organic matters were the decisive factor of the CA Vertisols apprearing black. However, the effects of the structures of the organic matters absorbed by the smectites on the color of the black organic-inorganic complexes remains unclear. Therefore, this study aims to explore the mechanism of these organic-inorganic complexes appearing black from the structural characteristics of the organic matters in the black organic-inorganic complexes and their relationships to smectites. Firstly, the physical method was adopted to extract the light-colored components (>53 μm particles, white (W) and light white (LW))) and black components (light black (LB), black (B) and nano black (NB)) from the topsoil layer (0～40 cm) of the typical CA Vertisols in three sites of the Huang-Huai-Hai Plain in China. The blackness, organic matter structures and smectite contents of the extracted components were then measured by Spectrophotometer, solid-state 13C NMR spectrometer and X-ray diffractometer. Finally, correlation analysis and path analysis of smectites, organic matter structures and soil blackness showed that the direct and indirect effects through alkyl C, carboxyl C, amino C and O-alkyl C on soil blackness are strong in all three soils, while both of the direct and indirect effects of aromatic C content and aromaticity on soil blackness are weak. Besides, the direct and the indirect effects through carboxyl C, amino C and alkyl C of smectites on soil blackness are also strong. Therefore, it is the carboxyl C, amino C, alkyl C and O-alkyl C, rather than the aromatic carbon and high aromaticity in the traditional view, that determine the black color of the CA Vertisols were by being selectively absorbed by the widely existing smectites in the CA Vertisols to form organic-inorganic complexes.