Molecular mechanisms of humus formation mediated by new ammonifying microorganisms in compost

Humus is the main product of organic waste composting in agriculture. The conversion of carbon and nitrogen in composting is controlled by ammonifying microorganisms (AM), but their role and mechanisms in humus formation are unclear. This study used multiple spectroscopic and microbiological techniques to explore how new ammonifying microorganism cultures (NAMC) molecularly affect humus formation in cow manure and straw compost. NAMC increased humus by 3.45 % - 9.46 %, resulting in enhanced humic acid and reduced fulvic acid. NAMC (especially Amm-4) also altered the chemical properties of humus, producing highly reactive amides and creating binding sites for low molecular weight compounds. NAMC enhanced the formation of O-H and C = O functional groups, which contributed to the formation of the aromatic structure and facilitated the threedimensional polymerization of humus. Furthermore, NAMC promoted the Maillard and lignin pathways of humus formation, as revealed by structural equation models. This study provides new insights into the molecular mechanisms of NAMC-mediated humus formation during composting.