玉米秸秆腐解过程中形成胡敏酸的组成和结构研究

CHEMICAL COMPOSITION AND STRUCTURE OF HUMIC ACID FROM COMPOSTED CORN STALK RESIDUE

采用化学方法和谱学方法对玉米秸秆腐解生成胡敏酸(CCSR HA)的组成和结构进行了研究。结果表明,CCSR HA的碳组成可分成三个部分:脂肪族碳、芳香族碳和羧基碳,它们的含量分别为59.62%、26.94%和13.44%。CCSR HA主要的官能团包括羟基、烷基、羧基、酰胺基、苯环、烷氧基及碳水化合物结构,木质素残体是其骨架,碳水化合物结构或类糖结构及烷基片段是其主要组成单元。其类型属于Rp型胡敏酸。未腐解的玉米秸秆本身就含有类胡敏酸物质(OCSR HA),OCSR HA和CCSR HA的官能团组成上有一定差异,后者结构中,甲基、亚甲基、次甲基、醚键官能团和酚羟基的含量降低,而酰胺成分、游离的羧基、甲氧基、碳水化合物组分相对含量升高,脂族性升高,芳香性降低,芳香度由初始的42.19降至腐解后的29.97,并且与无机物质的结合能力增强。就元素组成的变化看,CCSR HA中C和H元素的含量趋于降低,而N和O元素的含量趋于升高。CCSR HA同土壤胡敏酸相比,糖类结构含量较高,并且以片段的形式与水解木质素残体相连。羧基含量较低,但以不同的连接方式存在着。

Chemical composition and structure of humic acids extracted from composted corn stalk residue （CSR） were studied with the aid of Fourier transform infrared （FTIR） spectroscopy, 1^H and 13^C nuclear magnetic resonance（1^H-NMR, 13^C- NMR） spectroscopy and chemical analysis. The carbons in Humic acid from composted CSR （CCSR HA）can be mainly divided into three groups： aliphatic-C, aromatic-C and carbonyl-C, accounting for 59.62%, 26.94% and 13.44% of the total C, respectively. The major functional groups in the CCSR HA include hydroxyl, alkyl, carboxyl, amide, benzene ring, methoxyl, carbonyl and carbohydrate, with residual lignins being their skeleton and carbohydrates, and long-chain aliphatic structural groups their basic composition units. CCSA HA is of the Rp type of humic acids. In uncomposted corn stalks per se humic acids （ OCSR HA） can be found and it is somewhat different from CCSR HA in composition of functional groups. The latter is relatively lower in methyl, methylene, ether and phenol hydroxyl but higher in amide, free carboxyl, methoxyl and carbohydrate. Aromaticity of CCSR HA is 29.97, and significantly lower than that, 42.19, of OCSR, but the capacity of CCSR HA combining with inorganic matters becomes stronger. As far as variation of the elemental composition is concerned, the contents of C and H are lower and the contents of N and O are higher in CCSR HA as compared to what is in OCSR HA. Compared with soil HA, CCSR HA is significantly lower in aromaticity, but much higher in content of sugar-like components, which are not present as free carbohydrate, and instead are incorporated into structures such as hydMyzable lignins. CCSR HA is also comparatively lower in content of carboxyl groups, which exist in different forms.