CONTRIBUTIONS FROM DIFFERENT MICROBIAL PROCESSES TO N2O EMISSION FROMSOIL UNDER DIFFERENT MOISTURE REGIMES

Nitrous oxide emissions from a sandy-loam textured soil wetted to matr ic potentials of either -1.0 or -0.1 kPa were determined in laboratory experiments in which the soil was incubated in air (control), air plu s 10 Pa C2H2 (to inhibit nitrification), 100 kPa O-2 (to suppress deni trification), 10 kPa C2H2 (to inhibit N2O reduction to N-2 in denitrif ication) or following autoclaving. The total N2O production, consumpti on and net N2O emission from the soils together with the contributions to N2O emission from different processes of N2O production were estim ated. The rate of N2O production was significantly greater in the wett er soil (282 pmol N2O g(-1) soil h(-1)) than in the drier soil (192 pm ol 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 we tter 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 an d nitrification made only a small contribution (1% of the total N2O pr oduction) in the wetter soil. Denitrifying nitrifiers were the predomi nant source of N2O emitted from the drier soil and other (non-nitrifyi ng) denitrifiers were the predominant source of N2O emitted from the w etter soil.