Integrated isotopic labeling analysis unveils precise proportions of ammonia emissions during composting

Despite considerable research on ammonia emissions in composting, the precise proportion of these emissions remains undetermined through established technological methods. This study employs stable isotopic labeling techniques in conjunction with microbial sequencing and quantitative analysis of functional genes to assess the precise contribution and underlying causes of nitrogen loss. The results from tracking isotopic labeled amino acids reveal changes and emission characteristics in the initial nitrogen state of amino acids during composting. The most significant finding is the total nitrogen loss in composting, which amounts to 33.75 %. Within this, 21.31% is lost in the form of ammonia emissions, and 12.44 % is lost through leachate runoff. Statistical analysis of 15N in the compost pile indicates that the thermophilic stage is the primary phase for ammonia emissions. During this stage, the ammonia emission rate is 17.09% of the initial total nitrogen, constituting 80.20% of the overall ammonia emissions throughout the entire composting process. Similarly, liquid nitrogen loss exhibits the same trend. Microbiological analysis substantiates this conclusion, indicating that the reduction in ammonium ion conversion functionality (amoA gene) during the thermophilic stage leads to a significant volatilization of ammonia. The findings of this study contribute to an enhanced understanding of nitrogen loss in compost management, providing valuable insights for effective nitrogen conservation practices in composting.