Production of N₂O in soil during decomposition of dead yeast cells with different spatial distributions

Production and sources of N2O were determined in soil columns amended with autoclaved yeast cells either mixed into or added as 0.5 cm(3) lumps to the soil in combination with no or 200 mu g NO3--Ng(-1). At four occasions over a two-week study period, subsets of cores were measured for N2O production during 4-hour incubations under atmospheres of ambient air, 10 Pa of C2H2, and N-2, respectively. Denitrification enzyme activity (DEA) was assessed in subsamples of cores that had been incubated continuously under air.

Autoclaved yeast provided a C-source readily available for denitrifying bacteria in the soil. Nitrous oxide production was negligible in unamended columns whereas accumulated N2O losses in the presence of yeast material were substantial, varying between 15 to 49 ng N2O-Ng(-1)h(-1). Mixing yeast into the soil caused the highest production of N2O followed by the yeast lump and no yeast treatments. Incubation in the presence of 10 Pa C2H2 indicated that denitrification was the sole source of N2O, in accordance with an increase in DEA. Nitrous oxide production and DEA peaked after 4-7 days of incubation, and both were unaffected by additional NO3. Two to four-fold responses to anaerobiosis and accumulation of NO3- and NH4+ in proximity of the lumps indicated that N2O production here was limited by relatively low C-availability. In contrast, 10- to 12-fold responses to anaerobiosis and no accumulation of inorganic N suggested a higher C-availability where yeast was mixed into the soil.