Microbial-driven processes, including nitrification and denitrification closely related to soil nitrous oxide (N
2O) production, are orchestrated by a network of enzymes and genes such as
amoA genes from ammonia-oxidizing bacteria (
AOB) and archaea (
AOA),
narG (nitrate reductase),
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Microbial-driven processes, including nitrification and denitrification closely related to soil nitrous oxide (N
2O) production, are orchestrated by a network of enzymes and genes such as
amoA genes from ammonia-oxidizing bacteria (
AOB) and archaea (
AOA),
narG (nitrate reductase),
nirS and
nirK (nitrite reductase), and
nosZ (N
2O reductase). However, how climatic factors and agricultural practices could influence these genes and processes and, consequently, soil N
2O emissions remain unclear. In this comprehensive review, we quantitatively assessed the effects of these factors on nitrogen processes and soil N
2O emissions using mega-analysis (i.e., meta-meta-analysis). The results showed that global warming increased soil nitrification and denitrification rates, leading to an overall increase in soil N
2O emissions by 159.7%. Elevated CO
2 stimulated both
nirK and
nirS with a substantial increase in soil N
2O emission by 40.6%. Nitrogen fertilization amplified NH
4+-N and NO
3−-N contents, promoting
AOB,
nirS, and
nirK, and caused a 153.2% increase in soil N
2O emission. The application of biochar enhanced
AOA,
nirS, and
nosZ, ultimately reducing soil N
2O emission by 15.8%. Exposure to microplastics mostly stimulated the denitrification process and increased soil N
2O emissions by 140.4%. These findings provide valuable insights into the mechanistic underpinnings of nitrogen processes and the microbial regulation of soil N
2O emissions.
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