Nitrous Oxide Sources in Aerobic Soils: Nitrification, Denitrification and Other Biological Processes

Nitrous oxide (NrO) production in aerobic, intact soil cores collected from two forest sites was partitioned into different sources of N,O by subjecting soils to specitlc inhibitors during short-term incubations. We used acetylene (IO Pa) to selectively inhibit N,O production by nitrifiers, 100 kPa (100% v/v) 0, to inhibit N,O production by denitrifiers, and sterilixed soil to evaluate chemical sources of N,O. Individual soil cores were incubated in a recirculating atmosphere system under air, 100 kPa 0,. and air + IO Pa C,H, atmospheres for Gt h under each condition. Rates of N,O production in air ranged from 2.8 to 8.5 ng N g-t h-i in soils from the Rose Lake site and from 0.1 to 0.94 ng N g-i h-i in soils from Warren Woods. The importance of specific N,O sources in these soils varied among soil cores within each site. in the recently disturbed, more fertile Rose Lake site nitrifiers and denitrigers were both important N,O sources, but in many cores a si~i~nt portion of the N,O Run was inhibited by neither acetylene nor 0,. impiying an alternate N,O source. Sterilixed soil produced little N,O, which suggests that the alternate source is biological. In the old-growth Warren Woods site nitritiers were significant but relatively unimportant sources of N,O. Or consistently stimulated rather than inhibited NrO production in cores from this site. suggesting (a) that denitrifiers in this site are a sink for N,O produced by other sources, and (b) that most of the N,O produced in this site is from sources other than nitritication and denit~~tion, Biological sources of N,O other than nitrifiers and denit~fiers were not further identified, although low soil pH values suggest that fungi may be important.