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

Abstract

Production and sources of N₂O were determined in soil columns amended with autoclaved yeast cells either mixed into or added as 0.5 cm³ lumps to the soil in combination with no or 200 μg NO^¯ ₃-N g⁻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 N₂, 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-N g⁻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 NO^¯ ₃. Two-to four-fold responses to anaerobiosis and accumulation of NO^¯ ₃ and NH4⁺ ₄ 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.