Objective  Returning the decomposition products of rice straw into the field is an inevitable requirement for the protection of black soils. However, the rice straw is rich in lignin, and is difficult to be decomposed alone. Can the decomposing process of rice straw be accelerated by the promoting effect of the Maillard reaction substrates on the humus formation?

  Method  To answer the above scientific question, the method of indoor culture was adopted, with the rice straw as the tested object and an appropriate amount of MnO₂ powder was added. The treatments of single glucose (Glu), catechol (Cat), and glycine (Gly) solution, two mixed solutions (Glu-Cat, Glu-Gly, and Cat-Gly) and their mixed solution (Ms) were designed, with an equal volume of sterile water as the CK control. They were inoculated with a microbial inoculant, cultured at a constant temperature of 28 ℃ for 90 d, and dynamically sampled at 0, 30, 60 and 90 days for the humus composition analysis.

  Result  ① No matter whether the Maillard reaction substrate was added or not, the C contents of water-soluble substances (C_WSS) in the decomposition products of rice straw were all enhanced. In contrast, the addition of the mixed solution of three Maillard reaction substrates was more beneficial for the increase of C_WSS, followed by the addition of glycine solution. The exogenous addition of Maillard reaction substrates were more helpful for the decomposition of humin (Hu); ② Under the influence of adding Maillard reaction substrates and their mixed solution, the changes in the C contents of humic-extracted acid (C_HE) in the decomposition process of rice straw were different. The addition of the mixed solution of glucose and catechol had the greatest effect on the increase of C_HE, followed by the addition of glucose, while the additions of glycine and a mixed solution of glucose and glycine were not conducive to the formation of humic-extracted acid (HE). ③ The molecular structure of humic acid (HA) extracted from the decomposition process of rice straw was simple first and then became more complicated. The molecular structure of re-condensed HA was simpler. The addition of mixed solution of catechol and glycine was more conducive to the decomposition of HA and made the molecular structure of HA simple. Compared with the CK control, the other treatments, except for the mixed solution of catechol and glycine, could effectively inhibit the degradation of HA molecules, in which the effect of single addition of glucose was the best. It was more helpful to the molecular stability of HA, and could enhance the C_HA/C_FA ratio, so that the humus quality could be improved. While the addition of catechol was not conducive to improve the humus quality, but it was easier to promote the decomposition of Hu.

  Conclusion  The addition of Maillard reaction substrates was more helpful to the increase of C_WSS and the decomposition of Hu, and the addition of glucose was more conducive to the structural stability of HA molecules in the decomposition products of rice straw, and could effectively improve the humus quality.