Increased soil N2O emissions under natural gradient of atmospheric NH3 deposition

Regions near intensive livestock farms experience high atmospheric ammonia (NH3) deposition. However, the effects of this deposition on local soil nitrous oxide (N2O) emissions remain underexplored. This study investigated the effects of farm-originated NH3 deposition on soil N2O emissions and nitrogen-cycle genes. Soil N2O fluxes were measured downwind (50–500 m) of an intensive pig farm in central southern China. Laboratory incubations also tested the effects of the nitrogen form and soil moisture on these fluxes. Results showed that N2O emissions generally increased with NH3 deposition. Within a 500 m radius, total N2O emissions were estimated at 69.7 kg N yr−1, representing 1.3% of the total NH3-N deposited (5,400 kg N yr−1). N2O fluxes were positively correlated with NH3 deposition, soil ammonium (NH4+-N), and the abundance of ammonia-oxidizing archaea (AOA). This suggests that NH3 deposition increases N2O emissions, primarily by boosting AOA-mediated nitrification. Lab experiments confirmed that NH4+-N produced larger N2O fluxes than nitrate-N (NO3−-N) at 60% soil water-filled pore space. In conclusion, atmospheric NH3 deposition significantly increased soil N2O emissions near livestock farms, highlighting the need to consider its role in accelerating global warming.