Molecular mechanisms underlying the mitigation of nitrous oxide emissions by hyperthermophilic composting fertilizer

Nitrous oxide (N₂O) emissions associated with fertilized agricultural soils are a major source of greenhouse gases. While hyperthermophilic composting reduces N₂O emissions, how its products affect the niche distribution of nitrogen (N) cycling microorganisms and regulate N₂O source-sink mechanisms remains unclear, limiting its application in soil ecosystems and further technology development. To address this, we established a pot-based experiment with different organic fertilizer treatments: no fertilization (NF), hyperthermophilic composting fertilization (HTCF), and thermophilic composting fertilization (TCF). Using gas chromatography combined with metagenomic sequencing and binning approaches, we investigated the effects of HTCF on soil N₂O emissions and the associated microbial mechanisms. The results showed that organic fertilization significantly altered soil properties, influencing bacterial community succession and N₂O emissions. Compared to TCF (9.57 g), HTCF (14 g) increased pakchoi biomass by 47.02%. Meanwhile, HTCF (2835 mg m^-2) reduced N₂O emissions by 47.15% compared to TCF (5364 mg m^-2). HTCF decreased the abundance of N₂O-producing genes, including norB and nirK, thereby contributing to lower N₂O emissions. HTCF altered microbial community structure, resulting in a greater relative abundance of obligate N₂O-reducing bacteria carrying the nosZ gene, which could contribute to reduced N₂O emissions. HTCF significantly enriched microorganisms such as Nostoc, Rhizobium, Mesorhizobium, and Piscinibacter, maintaining a stable soil environment and promoting the smooth progress of N fixation and nitrification. These findings elucidate microbial mechanisms underlying HTCF-induced N₂O mitigation and provide a scientific basis for integrated fertilization strategies to reduce greenhouse gas emissions.