[Effects of Biochar-loaded Ammonia Nitrogen on Soil Carbon Emissions, Enzyme Activity, and Microbial Communities]

The form of soil nitrogen input significantly affects soil CO₂ emission. As a new form of nitrogen input, biochar-loaded ammonia nitrogen not only reduces the input of chemical nitrogen fertilizer in farmland but also reduces the cost of environmental treatment. It is of great significance to promote the zero growth of national chemical fertilizer, the prevention and control of farmland non-point source pollution, and the realization of the national goal of "carbon peak" and "carbon neutralization." Through an indoor culture experiment, the effects of different nitrogen input forms on soil carbon emission, enzyme activity, and microbial community were studied through four treatments:no fertilization (CK), single application of chemical nitrogen fertilizer (CF), biochar combined application of chemical nitrogen fertilizer (BF), and biochar-loaded ammonia nitrogen (BN). The results showed that compared with that in CF, BF significantly increased cumulative carbon emissions (66.24 %), whereas BN had no significant difference. It is worth noting that the cumulative carbon emissions were significantly reduced by 35.28 % compared with that in BF and BN. Compared with those in CF and BF, the activities of β-glucosidase, peroxidase, and polyphenol oxidase treated with BN significantly increased by 20.25 % and 5.20 %, respectively. Compared with that in CF, the BF treatment increased microbial community richness and community diversity, whereas the BN treatment decreased microbial community richness. Compared with that in BF, the relative abundance of Proteobacteria decreased by 11.16 %, and the relative abundance of Actinobacteria and Bacteroidota increased by 8.12 % and 5.83 %, respectively, in which xylosidase activity was the most important soil factor affecting microbial community structure. The relative abundance of Chloroflexi was significantly correlated with cellobiose hydrolase activity, and the relative abundance of Gemmatimonadetes was significantly correlated with β-glucosidase activity. There was a very significant correlation between the relative abundance of Proteobacteria and cumulative carbon emissions. To summarize, compared with those under biochar combined with chemical nitrogen fertilizer, biochar loaded with ammonia nitrogen significantly reduced cumulative carbon emissions, and its emission reduction effect was better. The results of this study will be beneficial to the landing of the national "double carbon strategy," the healthy development of the biological natural gas industry, the construction of the national green cultivation circular agriculture system, and the realization of the national zero growth strategy of chemical fertilizer.