Bacterial denitrification drives elevated N2O emissions in arid southern California drylands

Abstract

Soils are the largest source of atmospheric nitrous oxide (N2O), a powerful greenhouse gas. Dry soils rarely harbor anoxic conditions to favor denitrification, the predominant N2O-producing process, yet, among the largest N2O emissions have been measured after wetting summer-dry desert soils, raising the question: Can denitrifiers endure extreme drought and produce N2O immediately after rainfall? Using isotopic and molecular approaches in a California desert,we found that denitrifiers produced N2O within 15 minutes of wetting dry soils (site preference = 12.8 ± 3.92 per mil, δ15Nbulk = 18.6 ± 11.1 per mil). Consistent with this finding, we detected nitrate-reducing transcripts in dry soils and found that inhibiting microbial activity decreased N2O emissions by 59%. Our results suggest that despite extreme environmental conditions - months without precipitation, soil temperatures of≥40°C, and gravimetric soilwater content of <1% - bacterial denitrifiers can account for most of the N2O emitted when dry soils are wetted.

Citation

Krichels, Alexander H.; Jenerette, G. Darrel; Shulman, Hannah; Piper, Stephanie; Greene, Aral C.; Andrews, Holly M.; Botthoff, Jon; Sickman, James O.; Aronson, Emma L.; Homyak, Peter M. 2023. Bacterial denitrification drives elevated N2O emissions in arid southern California drylands. Science Advances. 9(49): eadj1989.