The effects of fire on biogenic soil emissions of nitric oxide and nitrous oxide

Measurements of biogenic soil emissions of nitric oxide (NO) and nitrous oxide (N 2 O) before and after a controlled burn conducted in a chaparral ecosystem on June 22, 1987, showed significantly enhanced emissions of both gases after the burn. Mean NO emissions from heavily burned and wetted (to simulate rainfall) sites exceeded 40 ng N m −2 s −1 , an increase of 2 to 3 compared to preburn wetted site measurements. N 2 O emissions from burned and wetted sites ranged from 9 to 22 ng N m −2 s −1 . Preburn N 2 O emissions from these wetted sites were all below the detection level of the instrumentation, indicating a flux below 2 ng N m −2 s −1 . The flux of NO exceeded the N 2 O flux from burned wetted sites by factors ranging from 2.7 to 3.4. These measurements coupled with preburn and postburn measurements of ammonium and nitrate in the soil of this chaparral ecosystem and measurements of NO and N 2 O emissions obtained under controlled laboratory conditions suggest that the postfire enhancement of NO and N 2 O emissions is due to production of these gases by nitrifying bacteria.