Relative importance between nitrification and denitrification to N₂ O from a global perspective

Nitrous oxide (N₂ O) is a potent greenhouse gas, and its mitigation is a pressing task in the coming decade. However, it remains unclear which specific process between concurrent nitrification and denitrification dominates worldwide N₂ O emission. We snagged an opportunity to ascertain whence the N₂ O came and which were the controlling factors on the basis of 1315 soil N₂ O observations from 74 peer-reviewed articles. The average N₂ O emission derived from nitrification (N₂ O_n ) was higher than that from denitrification (N₂ O_d ) worldwide. The ratios of nitrification-derived N₂ O to denitrification-derived N₂ O, hereof N₂ O_n :N₂ O_d , exhibited large variations across terrestrial ecosystems. Although soil carbon and nitrogen content, pH, moisture, and clay content accounted for a part of the geographical variations in the N₂ O_n :N₂ O_d ratio, ammonia-oxidizing microorganisms (AOM):denitrifier ratio was the pivotal driver for the N₂ O_n :N₂ O_d ratios, since the AOM:denitrfier ratio accounted for 53.7% of geographical variations in N₂ O_n :N₂ O_d ratios. Compared with natural ecosystems, soil pH exerted a more remarkable role to dictate the N₂ O_n :N₂ O_d ratio in croplands. This study emphasizes the vital role of functional soil microorganisms in geographical variations of N₂ O_n :N₂ O_d ratio and lays the foundation for the incorporation of soil AOM:denitrfier ratio into models to better predict N₂ O_n :N₂ O_d ratio. Identifying soil N₂ O derivation will provide a global potential benchmark for N₂ O mitigation by manipulating the nitrification or denitrification.