Mechanisms Of Biochar On Nitrous Oxide Production In Agricultural Soils:A Meta-analysis And A Validation Study

Nitrous oxide（N₂O）as a greenhouse gas has a warming potential 300 times stronger than carbon dioxide（CO₂）,and N₂O emissions from the widespread use of nitrogen fertilizers in agricultural systems contribute more than 20%of the total N₂O,contributing to the greenhouse effect and loss of nitrogen（N）.Therefore,an in-depth study of the mechanisms of soil nitrogen transport and transformation is essential to reduce N₂O emissions from agricultural fields and enhance nitrogen use efficiency.Biochar has been shown to regulate soil N₂O emissions by directly or indirectly influencing microbial growth metabolism,while the mechanism of biochar influence on the microbial pathway of N₂O production is unclear.In this study,the main effects of biochar addition on N₂O production processes in agricultural soils were macroscopically evaluated by a big data analysis,and based on this,experiments were designed to validate and carry out microbial mechanism analysis,using root box experiments planting chard with two levels of low and high nitrogen and different biochar application rates.The changes of biochar input on bacterial and fungal community structure,gene abundance and latent potential related to N₂O production were investigated to reveal the microbial mechanisms of biochar affecting soil N₂O production process.The main research findings are as follows:（1）Meta-analysis integrating 569 sets of observations from 48 papers showed that biochar addition significantly increased soil p H（4.58%）,SOC（42.15%）,and reduced NH₄⁺-N（14.56%）and N₂O fluxes（23.96%）.Biochar can directly or indirectly affect microbial functional groups associated with N₂O production,but it is difficult to directly correlate biochar production conditions（feedstock,pyrolysis temperature）and characteristics（C/N ratio,p H）with N₂O;the effect of biochar on N₂O was more dependent on the application rate（Q_b=7.56,P=0.003）,and biochar application rates above 40 tha^-1 reduced N₂O emissions by 30.48%.Increasing biochar dosage could limit denitrification N₂O production and promote N₂O reduction through nos Z,but the exact microbial mechanism needs to be further verified.（2）Biochar addition trials on typical vegetable soils showed that biochar increased soil p H(R_adj²=0.74,P<0.001)and carbon content(R_adj²=0.37,P=0.036).Bacterial diversity increased with increasing biochar application rate,while 1%biochar elevated fungal diversity most significantly.Soil carbon levels were significantly correlated with fungal and bacterial community structure,and changes were better explained using species utilization characteristics of the substrate.Biochar affected bacterial community structure mainly through environmental variables（p H）,but could have a direct effect on fungal communities.（3）Increasing the rate of biochar application reduced fast-acting N content and reduced bacterial denitrification potential by 14.62%,reducing unnecessary N losses from the soil.The addition of biochar directly increased the contribution of fungi to nitrification and denitrification activity（57.8%,70.0%,respectively）.Under biochar-nitrogen fertilizer pairing conditions,fungal enzyme activity explained more of the soil N conversion and biochar was a more important factor influencing soil nitrification and denitrification activities.This study confirms the advantages of biochar in reducing emission potential and improving soil health,and biochar reduces environmental emissions by directly increasing fungal enzyme activity,weakening bacterial activity and contributing to N2O production and possibly promoting N₂O reduction,providing a theoretical basis for the rational application of biochar in on-farm microecological regulation and agricultural production.