The impact mechanism of Manno-oligosaccharides on ammonia oxidation and microbial communities during aerobic composting

Abstract

The ammonium oxidation process is a critical step in the nitrogen cycle during aerobic composting, affecting the efficiency of nitrogen transformation and the quality of the compost. This study employed quantitative PCR and high-throughput sequencing to investigate the effects of different concentrations of Manno-oligosaccharides (MOS) (0.1 %, 0.5 %, 1.0 %, and 2.0 %) on nitrogen dynamics and ammonia-oxidizing microbial communities in composting cattle manure and straw, with a control. The results indicated that different concentrations of MOS increased the peak temperatures during the thermophilic stage of composting to above 60°C, higher than that of the CK (57.4°C), while ensuring that all treatments met the requirements for harmless disposal. Particularly, the germination index (GI) of the 0.5 % manno-oligosaccharide treatment reached 109.3 %, demonstrating excellent treatment efficacy. The 0.5 % manno-oligosaccharide treatment significantly increased the NO₃^--N content in compost (P < 0.05). The copy number of AOB amoA gene in the M0.5 and M1 treatments during the compost maturation stage was significantly higher than that in other treatments. Norank_p_environmental_samples and Nitrosomonas are the dominant microorganisms driving ammonia oxidation in the compost. Especially in the treatment with 0.5 % MOS, they play a crucial role in the immobilization of ammonia nitrogen. Structural equation modeling (SEM) analysis showed a significant positive correlation between AOB amoA genes and NO₃^--N in the 0.5 % oligosaccharide treatment, indicating effective promotion of nitrogen conversion by ammonia-oxidizing bacteria in the compost. These findings highlight the potential of manno-oligosaccharide as a biological modifier to improve composting efficiency and nitrogen management.