Wildfires drive trade-offs in ammonia-oxidizing groups and promote denitrification to increase soil emissions of nitric oxide (NO) and nitrous oxide (N 2 O) in California chaparral
Year: 2026
Type: preprint
Abstract: Wildfires can promote trade-offs in soil nitrifier and denitrifier communities that affect post-fire nitrogen (N) cycling and emissions of nitric oxide (NO), nitrous oxide (N 2 O), and dinitrogen (N 2 ). For example, by increasing soil pH and ammonium (NH 4 + ), wildfires could increase the abundance of ammonia-oxidizing bacteria (AOB) over archaea (AOA). Because AOB and AOA process N differently, nitrifier trade-offs may affect N emissions and nitrate (NO 3 - ) supply with downstream effects on denitrifier activity, leading us to ask: Do trade-offs between AOA and AOB abundance and shifts in denitrifying processes influence N emissions over time after wildfire? We selectively inhibited AOA and AOB communities from soil collected over four seasonal time points one year before and after a chaparral wildfire and used stable isotopes to parse denitrifier contributions to N 2 O emissions. Over one year after the wildfire, soil pH increased from 6.1 to 7.0, soil extractable NH 4 + increased 30-fold, NO 3 - increased 5-fold, and NO 2 - increased 9-fold. AOB amoA gene copy numbers increased 20-fold one year after fire, while AOA abundance remained unchanged. Post-fire soil NO emissions increased 63-fold over one year, with varied contributions from all nitrifier groups. Soil N 2 O emissions peaked eight months after fire (2271 ± 634 ng N 2 O-N g -1 soil), with increased contributions from AOA. Wildfire increased δ 15 N SP N2O and δ 15 N bulk N2O values, suggesting increased N 2 O reduction to N 2 . Overall, wildfire increased AOB abundance relative to AOA, promoting nitrification activity and providing intermediates to denitrifiers to increase emissions of NO and N 2 O for up to one year after fire.
Language: English
Subfield: Soil Science
Domain: Life Sciences
SDGs: Life on land, Climate action
Open Access status: green
OpenAlex ID: W7213311635