Bacterial denitrification drives elevated nitrous oxide emissions in arid southern California drylands
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 the largest N2O emissions have been measured after wetting summer-dry desert soils. This raises 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. Consistent with this finding, we detected NO3-reducing transcripts in dry soils and found that inhibiting microbial activity decreased N2O emissions by 59 percent. Our results suggest that despite extreme environmental conditions—months without precipitation, soil temperatures ≥ 40°C, and gravimetric soil water content < 1 percent—bacterial denitrifiers can account for most of the N2O emitted when dry soils are wetted.
These results suggest that denitrification may be an overlooked source of N2O in dryland ecosystems. We also show that the abundance of bacteria that can carry out denitrification may relate to peak N2O emissions, suggesting that understanding the distribution of these bacteria may help predict where dryland N2O emissions are greatest.