Farmed soil is considered to contribute more than 60% anthropogenic N2O emission which plays critical role in global warming potential. Straw-based hydrogels with abundant functional groups are commonly used in environmental and agronomic applications primarily as adsorbents. Those functional groups could mediate electron transfer in the process of adsorbates and might also regulate N2O emission. However, it was still unclear whether and how these functional groups affect the process. To address this knowledge gap, we employed spectral analysis and a robotized incubation system to determine mechanisms of different functional groups in influencing soil N2O. The results indicated that the straw-based hydrogel was capable of significantly reducing the emission of N2O in denitrification, and the electrochemical properties of the hydrogel had promoting effect of the microbial genetic potential for N2O reduction. Specifically, carboxymethyl (R-COO) and primary amine groups (R-NH2) promoted complete denitrification through electron supply. Furthermore, R-NH2 had a significant negative correlation with N2O emissions. To further verify the role of specific structures and functional groups in denitrification, we conducted an experiment using pure lignin as a template. This experiment resulted in an increase in R-NH2 content to 13.2% and a decrease in N2O emissions by 49.1% compared with straw hydrogel. These results prove the feasibility of straw-based hydrogel as a redox system to accelerate complete denitrification, and the electron-donating functional groups were significantly related to the reduction rate of N2O. Finally, based on these mechanisms, functional group targeted grafting technology was proposed to improve its ability to mitigate N2O emission reduction.
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