Analysis Of Soil Humus Components By PY-GC-MS

Humus is a mixture composed of a series of macromolecular organic matter with different molecular weights.After years of research,the study of soil humus in terms of extraction grouping,formation source and function has a certain foudation,but its composition still needs to be explored.In this paper,two groups of soil humus components(humic acid(HA),fulvic acid(FA))were obtained by chemical extraction.The organic matter content and pyrolysis characteristics of humus components of tobacco planting soils with different acidities in Tengchong area were preliminarily discussed by thermal analysis.PY-GC-MS was used to further explore the differences in its composition and screen out the potential characteristic markers of each component of humus,providing a theoretical basis for soil acidity improvement and regulation in Tengchong area and "humus omics".Research indicated:(1)HA extracted from acid soil(p H4.5-7.0)and HA extracted from alkaline soil(p H7.0-8.5)at 150-430℃,the weight loss was 41.72% and 42.44% respectively,which was the content of small molecules.At 430-550℃,the weight loss was 10.15% and 14.94%respectively,which was the content of aromatic structures.The pyrolysis stage of FA was mainly divided into two stages,the first stage was175-400 ℃,the second stage was 400-500 ℃.In the first stage of pyrolysis,FA extracted from acid soil and FA extracted from alkaline soil losed the weight were 22.14% and22.99% respectively,which was the content of smaller molecular substances outside the aromatic core.In the second stage of pyrolysis,the weight loss was 10.58% and 4.93%respectively,which is the content of aromatic structural substances.According to the DTG curve,it was found that the FA extracted with different acidity was different in the second stage of pyrolysis.The FA extracted from acid soil showed two smaller weightless peaks,while the FA extracted from alkaline soil only showed one weightless peak.Therefore,the FA extracted from acid soil was different from the FA extracted from alkaline soil in the high temperature region.The HA reaction mechanism function of acid soil extraction was three-dimensional diffusion,and the other three components were random nucleation and subsequent growth.(2)The optimal pyrolysis temperature(500°C)and single-step residence time(0.2min)of PY-GC-MS were determined by the number of pyrolysis product peaks and substance types.The results showed :Among the pyrolysis products,HA contains a large number of types of lignin and aliphatic hydrocarbon compounds.Four potential characteristic markers were screened using multivariate statistical methods such as PCA and OPLS-DA,among which Methyl stearate was a potential characteristic marker shared by HA and FA.The content of Ethanone,1-(3,4,5-trimethoxyphenyl)(8.64%)in HA extracted from acid soil was lower than that of HA extracted from alkaline soil(15.17%),but in the HA extracted from acid soil,the content of Hexadecanoic acid methylester,9-Octadecenoicacid,methylester,(E)-and Methyl stearate(10.58%,4.28%,8.40%)were higher than the content of HA extracted from alkaline soil(4.09%,1.96%,2.98%).Among the pyrolysis products,FA contains many types of FA nitrogen-containing compounds and aliphatic hydrocarbon compounds.Six potential characteristic markers were screened using multivariate statistical methods.The content of DL-Proline,5-oxo-,methylester,9-Octadecenamide,(Z)-,and Methyl stearate,in FA extracted from acid soil(17.00%,13.13%,12.97%)were significantly higher than that of FA extracted from alkaline soil(8.43%,6.23%,7.97%),but the content of 2-Cyclopenten-1-one,3-ethyl-2-hydroxy-and 2-Methyltetracosane content in FA extracted from acid soil(1.73%,1.95%)were significantly lower than the content of FA extracted from alkaline soil(5.16%,6.22%),but Thiocarbamicacid,N-cyclohexyl-,S-(2,5-dihydroxyphenyl)ester has no significant difference.