1. College of Biological Science and Technology, Yili Normal University, Yili 835000, China
2. College of Resources and Environment, China Agricultural University, Beijing 100193, China
3. Institute of Organic Cycle Research, China Agricultural University (Suzhou), Suzhou 215100, China
4. Beijing Fertile Tiandi Biotechnology Co., Ltd., Beijing 100193, China
Abstract：The process by which organic matter is transformed and polymerized into humus through biological or chemical conversion is called humification. Both biological and abiotic pathways can drive this process. The abiotic pathway offers several advantages, including environmental friendliness, excellent catalytic performance, and controllable reaction conditions. It plays an important role in enhancing soil fertility, regulating pollutants, and improving compost quality. However, because microorganisms in compost are the primary driving force for organic matter transformation and play a dominant role, the abiotic pathway is often overlooked. Amino acids are the core structural components of humic acid substances and act as precursor substances in the abiotic pathway, participating in the phenolic protein and Maillard systems, and promoting the polymerization of small organic monomer molecules to form humic acid substances. Previous studies have shown that the formation of humus generally requires the participation of amino acids in the synthesis reaction, continuously condensing to form large molecular polymers. However, the effects of different amino acid types and concentrations on abiotic humification remain unclear. Therefore, in this study, catechol and glucose were used as the reaction substrates for the phenolic protein pathway and the Maillard pathway, respectively. The extraction solutions of the reaction products were analyzed by ultraviolet-visible spectroscopy and three-dimensional fluorescence spectroscopy. The aim was to elucidate the mechanism of amino acid precursor substances on the abiotic formation of humic acid and to investigate the effects of various types and concentrations of amino acids on the humification process. The results showed that at the end of the reaction, the concentration of humic acid-like substances (HLA) in the phenolic protein theoretical system with lysine participation was the highest, reaching 120 mg·L-1. In the Maillard systems with different amino acids, only the tryptophan addition system showed accumulation of HLA, indicating that aromatic amino acids are conducive to the direct synthesis of humic acid-like substances in the Maillard system. Ultraviolet-visible absorption spectroscopy and three-dimensional fluorescence spectroscopy indicated that lysine made a greater contribution to the aromatization degree of humic acid in the abiotic synthesis pathway. With the increase in lysine concentration, the content of fulvic acid-like substances (FLA) in each abiotic humic acid formation system also increased. When the lysine concentration was 0.025 and 0.05 mol·L-1, HLA was produced in the phenolic protein system at 24 hours into the reaction. Under the same lysine concentration, the Maillard theoretical pathway had the highest FLA content at the end of the reaction. In contrast, the phenolic protein system yielded the highest HLA and had the highest humic-to-fulvic acid ratio (DP). A comprehensive analysis indicated that the phenolic protein system had a more effective impact on the abiotic synthesis of humic acid compared to the Maillard system. This study revealed the influence of amino acid types and concentrations on the humification process of compost, providing theoretical support for further regulating the degree of compost humification and enhancing the synthesis of humic acid under the phenolic-protein theory.
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