Mechanism of oligosaccharides on nitrogen and ammonia-oxidizing microbial communities in aerobic composting processes

Abstract To explore the effects of oligosaccharides on nitrogen and ammonia-oxidizing microbial communities during aerobic composting of cattle manure and straw, this study conducted composting experiments with four concentrations of oligosaccharides: 0.1% (M0.1), 0.5% (M0.5), 1.0% (M1), and 2.0% (M2), along with a control group (CK). The results indicated that different concentrations of oligosaccharides increased the peak temperatures during the thermophilic phase 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 GI value of the 0.5% oligosaccharide treatment reached 109.3%, demonstrating excellent treatment efficacy. The 0.5% oligosaccharide treatment significantly increased the NO₃-N content in compost (P < 0.05), thereby enhancing nitrogen content. AOB amoA functional gene detection identified two dominant ammonia-oxidizing bacteria, Nitrosomonas and Nitrosospira, with Nitrosomonas primarily present in the 0.5% oligosaccharide treatment, playing a crucial role in ammonia nitrogen fixation. 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. In conclusion, the addition of 0.5% oligosaccharides can increase the dominance of AOB genera, enhance nitrogen transformation during composting, provide more available nitrogen sources for crops, and thereby improve nitrogen fertilizer utilization efficiency.