长期玉米连作下黑土各组分有机质化学结构特征

【目的】研究玉米连作24年前后黑土有机质红外光谱特征，探明长期玉米连作对黑土各团聚体及密度组分中有机质结构的影响，完善长期连作下土壤有机质化学结构动态变化理论。【方法】以中国科学院海伦农业生态试验站长期定位试验为研究平台，选取24年玉米连作下耕层（0-20 cm）土壤为研究对象，以试验设置前土样为对照，根据团聚体和密度大小，将土壤有机质进行分级，分别用元素分析仪和傅里叶红外光谱仪测定原土、各粒级团聚体及密度组分中的碳含量和有机质的红外光谱，对比分析玉米连作24年前后土壤有机质含量及红外光谱特征。【结果】玉米连作24年后，全土中碳含量降低5.3%，2-0.25 mm团聚体中碳含量显著降低，其他粒级团聚体中有降低的趋势；LF(游离态轻组)中碳含量增加32.74%，OF（闭蓄态轻组）中减少16.72%，MF（矿质结合态组分）中没有显著变化。土壤有机质中脂肪族-CH、多糖C-O、酚醇-OH吸收峰相对强度增强，芳香族C=C和羧基C=O吸收峰相对强度降低，脂肪族-CH/芳香族C=C比值增加。在各粒级团聚体中，-CH/C=C比值增加主要表现在＞2 mm团聚体中，主成分分析也表明＞2 mm团聚体中有机质结构变化最大，该粒级团聚体中3个密度组分LF、OF和MF有机质-CH/C=C比值增加，且LF中增加程度最大；在其他粒级中的3个密度组分有机质-CH/C=C比值有增加的趋势。【结论】长期玉米连作，黑土大粒级团聚体和各密度组分中有机质结构趋于脂肪化、简单化，团聚体和矿物质结合对有机质的保护作用降低，黑土有机质稳定性下降。

Chemical Structure Characteristics of All Fractionations in Mollisol Organic Matter Under Long-Term Continuous Maize Cropping

【Objective】 The objective of this paper is to reveal the effects of 24-year continuous maize cropping on Mollisol organic matter structure in all classes aggregates and density fractionations through studying infrared spectra characteristics of Mollisol organic matter before and after setting experiments, which can supplement soil organic matter (SOM) chemical structure dynamic theory under long-term continuous cropping.【Method】 Soil samples were obtained under 24-year continuous maize cropping in Hailun Agro-ecology Field Research Station, Chinese Academy of Sciences. SOM were divided according to aggregate class and density, and measured carbon content and infrared spectra of SOM in all aggregates and density fractions by Element Analyzer and Fourier Infrared Spectrometer separately. The spectra of SOM before and after continuous maize cropping were compared and analyzed.【Result】 After 24-year continuous cropping, carbon content in bulk soil decreased by 5.3%, carbon content in 2-0.25 mm aggregates significantly decreased, the carbon content had the decreasing trend in other class aggregates; free light fractionation (LF) carbon content significantly increased by 32.74%, but in occluded light fractionation (OF) significantly decreased by 16.72%, while no significant change in mineral-associated fractionation (MF). The relative intensity of aliphatic -CH, polysaccharide C-O, phenolic alcohol -OH increased, while the relative intensity of aromatic C=C and carboxyl C=O decreased, the ratio of -CH/C=C increased. The ratio of -CH/C=C mainly increased in ＞2 mm, of which -CH/C=C value of three density fractionations increased, especially LF; while in the density fractionations of other class aggregates had increasing trend. 【Conclusion】 So Mollisol organic matter structure became aliphatic and simple under long-term continuous maize cropping, the protection abilities of aggregates and mineral association decreased under long-term continuous maize cropping, which can’t benefit for the stability and storage of organic matter.