Wildfire alters nitrogen cycling to increase soil emissions of nitric oxide (NO) and the heterogeneity of nitrous oxide (N2O) in California chaparral
| Authors: | Elizah Z. Stephens, M. Fabiola Pulido Barriga, Aral C. Greene, Alexander Krichels, Meg Kargul, Loralee Larios, Sydney I. Glassman, Peter M. Homyak |
| Year: | 2026 |
| Type: | Scientific Journal |
| Station: | Rocky Mountain Research Station |
| DOI: | https://doi.org/10.1016/j.geoderma.2026.117807 |
| Source: | Geoderma |
Abstract
Wildfires drive ecosystem nitrogen (N) loss globally through combustion of plant biomass and by depositing Nrich ash onto soils to stimulate emissions of nitric oxide (NO) and nitrous oxide (N2O)—trace gases that affect air quality and climate. However, spatial and temporal variation in post-fire soil NO and N2O emissions remain under-explored, motivating our hypothesis that emissions would vary temporally with plant and microbial successional changes and spatially with burn severity, available N, soil physicochemical properties, and microbial activity. We sampled burned and unburned soils seasonally over three years after a chaparral wildfire and found that soil NO emissions significantly increased by 80 ng NO-N g- 1 soil (cumulative 40-h incubations), with the highest emissions measured in year one from plots that burned at medium and high severities. No significant mean effects of burning were detectable for N2O emissions over three years (average 224 ng N2O-N g- 1 soil, burned; 30 ng N2O-N g- 1 soil, unburned); however, only burned soils produced statistical outlier fluxes of N2O that were up to ~ 165 × higher than the average in unburned soils. Isotopic characterization of N2O from highemitting soils indicated contributions from diverse processes, including nitrification and fungal and bacterial denitrification, pointing to heterogeneity in the post-fire environment that may generate hotspots of N2O production. Overall, increased soil NO and high N2O emissions post fire indicate that wildfires interact with soil N cycling to promote burn-severity-sensitive gaseous N losses years after the fires burn.