Contributions from different microbial processes to N2O emission from soil under different moisture regimes

Nitrous oxide emissions from a sandy-loam textured soil wetted to matric potentials of either -1.0 or -0.1 kPa were determined in laboratory experiments in which the soil was incubated in air (control), air plus 10 Pa C2H2 (to inhibit nitrification), 100 kPa O-2 (to suppress denitrification), 10 kPa C2H2 (to inhibit N2O reduction to N-2 in denitrification) or following autoclaving. The total N2O production, consumption and net N2O emission from the soils together with the contributions to N2O emission from different processes of N2O production were estimated. The rate of N2O production was significantly greater in the wetter soil (282 pmol N2O g(-1) soil h(-1)) than in the drier soil (192 pmol N2O g(-1) soil h(-1)), but because N2O consumption by denitrifiers was also greater in the wetter soil, the net N2O emissions from the wetter and the drier soils did not differ significantly. Non-biological sources made no significant contribution to N2O emission under either moisture regime and biological processes other than denitrification and nitrification made only a small contribution (1% of the total N2O production) in the wetter soil. Denitrifying nitrifiers were the predominant source of N2O emitted from the drier soil and other (non-nitrifying) denitrifiers were the predominant source of N2O emitted from the wetter soil.