Wildfires drive trade-offs in ammonia-oxidizing groups and promote denitrification to increase soil emissions of nitric oxide (NO) and nitrous oxide (N2O) in California chaparral
- 1University of California Riverside
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 (N2O), and dinitrogen (N2). For example, by increasing soil pH and ammonium (NH4+), 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 (NO3-) 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 N2O emissions. Over one year after the wildfire, soil pH increased from 6.1 to 7.0, soil extractable NH4+ increased 30-fold, NO3- increased 5-fold, and NO2- 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 N2O emissions peaked eight months after fire (2271 {+/-} 634 ng N2O-N g-1 soil), with increased contributions from AOA. Wildfire increased {delta}15NSPN2O and {delta}15NbulkN2O values, suggesting increased N2O reduction to N2. Overall, wildfire increased AOB abundance relative to AOA, promoting nitrification activity and providing intermediates to denitrifiers to increase emissions of NO and N2O for up to one year after fire.
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BibTeX
@misc{stephens2026wildfires,
title = {{Wildfires drive trade-offs in ammonia-oxidizing groups and promote denitrification to increase soil emissions of nitric oxide (NO) and nitrous oxide (N2O) in California chaparral}},
author = {E. Z. Stephens and A. H. Krichels and A. C. Greene and S. Zhao and C. Reid and J. Irby and M. E. Ordonez and D. Lewicka-Szczebak and E. J. Hanan and S. I. Glassman and P. M. Homyak},
howpublished = {bioRxiv},
year = {2026},
month = sep,
doi = {10.64898/2026.09.10.749748},
url = {https://www.biorxiv.org/content/10.64898/2026.09.10.749748v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Wildfires drive trade-offs in ammonia-oxidizing groups and promote denitrification to increase soil emissions of nitric oxide (NO) and nitrous oxide (N2O) in California chaparral
AU - E. Z. Stephens
AU - A. H. Krichels
AU - A. C. Greene
AU - S. Zhao
AU - C. Reid
AU - J. Irby
AU - M. E. Ordonez
AU - D. Lewicka-Szczebak
AU - E. J. Hanan
AU - S. I. Glassman
AU - P. M. Homyak
PY - 2026
DA - 2026/09/10
PB - bioRxiv
DO - 10.64898/2026.09.10.749748
UR - https://www.biorxiv.org/content/10.64898/2026.09.10.749748v1
AB - 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 (N2O), and dinitrogen (N2). For example, by increasing soil pH and ammonium (NH4+), 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 (NO3-) 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 N2O emissions. Over one year after the wildfire, soil pH increased from 6.1 to 7.0, soil extractable NH4+ increased 30-fold, NO3- increased 5-fold, and NO2- 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 N2O emissions peaked eight months after fire (2271 {+/-} 634 ng N2O-N g-1 soil), with increased contributions from AOA. Wildfire increased {delta}15NSPN2O and {delta}15NbulkN2O values, suggesting increased N2O reduction to N2. Overall, wildfire increased AOB abundance relative to AOA, promoting nitrification activity and providing intermediates to denitrifiers to increase emissions of NO and N2O for up to one year after fire.
ER -