应用~(13)C核磁共振技术研究土壤有机质化学结构进展

土壤有机质化学结构对准确评价土壤有机质的稳定性及其在土壤中的功能具有重要意义。土壤有机质化学结构的研究方法中,固态~(13)C核磁共振波谱技术(Solid-state ~(13)C-NMR spectroscopy)具有独特优势,对土壤有机质化学结构的解析更贴近真实状态,近年来已取得诸多新进展和新突破。综述了近年来应用~(13)C-NMR测定土壤全土、团聚体和密度组分、腐殖质组分的有机碳化学结构特征,分析了影响化学结构变化的因素。不同气候条件、植被类型、土地利用管理方式、土壤类型、土壤有机碳含量的全土中有机碳化学结构比较相似,均表现为烷氧碳比例最高,其次为烷基碳和芳香碳,羧基羰基碳比例最低。土壤有机碳主要来源于外源植物残体,植物残体化学结构的相似性可能是导致土壤有机碳化学结构相似的主要原因,环境条件、土壤自身属性和微生物活性的差异使土壤有机碳化学结构产生微小差异。土壤颗粒及化学组分间的有机碳分子结构差异较大,大颗粒有机碳中烷氧碳比例最高,小粒径及与矿物颗粒结合的有机碳中烷基碳和羧基羰基碳比例更高,粉黏粒和腐殖酸组分的有机碳化学结构在土壤类型间差异较大。今后的研究重点应更多地关注土壤有机质来源的定量化分析、土壤微生物对土壤有机碳组分和结构稳定性的贡献及调控机制、土壤有机碳稳定性的生物物理化学保护机制、空间大尺度环境因子/土壤生态过程与微观尺度的有机碳化学分子结构的耦合作用机制、跨学科的多种土壤有机碳化学分子结构测定辨识技术等方面的研究。

Advancement in Research on Application of 13C NMR Techniques to Exploration of Chemical Structure of Soil Organic Matter

The knowledge about chemical structure of soil organic matter (SOM) is crucial to accurate assessment of stability and function of SOM in the soil ecosystem. In the study on chemical structure of soil organic matter, the technology of solid-state ¹³C nuclear magnetic resonance (NMR) spectroscopy possesses a unique advantage of being capable of depicting chemical structure of nature soil organic matter, nondestructively and state-of-the-artly. Although extensive studies have been carried out on stability and molecular structure of SOM at a regional-climatic belt and ecosystem-community scale, little has been documented about chemical characteristics of SOM and its relationships with environmental factors at the global scale. This study presents a review on uses of the ¹³C NMR technology in determining chemical structures of organic carbons in bulk soil, soil aggregates, density fractions and humus components, and analyzes factors that alter the chemical structure of SOM. Organic carbons in bulk soils, regardless climate conditions, type of vegetation, land use pattern, soil type and content of organic carbon in the soil, were quite similar in chemical structure, all being the highest in O-alkyl C, which was followed by alkyl C, aromatic C, and carbonyl C in the end. It is widely accepted that soil organic carbon is mainly derived from plant residues, which are quite similar in chemical structure, so that soil organic carbons are similar in chemical structure, too. Differences in environment condition, soil property and microbial activity may cause some variations, but very minor, of the chemical structure of soil organic carbon, and the variations in soil particles and chemical components of the soil are quite significant. O-alkyl C abundance of the organic carbon is the highest in large-sized soil particles, while alkyl and carbonyl C are in small-sized or mineral associated particles. Chemical structure of organic carbon in silt-clayed particles and humic acid components vary quite sharply between soils different in type. Future researches should focus on quantitative analysis of SOM sources, contribution of soil microbes to the composition of SOM and stability of its structure and regulatory mechanisms, biophysico-chemical protection mechanisms of soil organic carbon stability, coupling mechanisms of spatial large-scaled environmental factors/soil ecological processes with microscopic scaled molecular structure of soil organic carbon, and interdisciplinary means and techniques to determine chemical structure of soil organic carbon.