Opdyke, M., R. Sutka, N. Ostrom, P. Ostrom, and H. Gandhi
Presented at the ASM at Estes Park (2006-09-01 to 2012-09-23 )
Nitrous oxide (N2O) production from terrestrial ecosystems has gained considerable attention due to an increase in the atmospheric concentration of this greenhouse gas and its ability to catalyze stratospheric ozone degradation. Since it is an intermediate of nitrite and nitrate reduction (denitrification) as well as a by-product of the oxidation of hydroxylamine to nitrite (nitrification), it is feasible to identify the sources of N2O fluxes by taking advantage of the differences in these two microbial processes. By examining the intramolecular distribution (isotopomers) of 15N in N2O produced from bacteria cultures, we have previously demonstrated that N2O from nitrification yields a site preference (difference between the central and terminal N atom in N2O) of 33 ‰ compared to 0 ‰ from denitrification. These results progressed to a field study from 2004 to 2006 at the Kellogg Biological Station LTER measuring soil N2O fluxes and isotopomers in treatment plots managed with conventional agriculture and successional (tilled and untilled) techniques. Nitrous oxide was collected from soil chambers placed 5 cm deep and covered with a lid. The chambers were vented to the atmosphere by a 0.5 m length of stainless steel tubing. Gas samples were collected in pre-evacuated 250 mL glass bottles with butyl rubber septum through peek tubing fitted with a syringe needle. Given our estimates from 2004 and 2005 of microbial processes using site preference, N2O was predominantly from denitrification following initial cultivation of soils. In 2006, we measured N2O fluxes and isotopomers in tilled and untilled mid-successional plots, a conventional agriculture field further treated with liquid manure and compared mid-successional to conventional agriculture treatments. In mid-May, site preference for soil-derived N2O was insignificant between the untilled mid-successional (11.9 to 16.1 ‰) and conventional agriculture (10.1 to 17.6 ‰) treatments, while soil treated with liquid manure exhibited a predominance of denitrification (1.8 to 2.8 ‰). Nitrous oxide measurements in early-June were constrained by low rainfall, with N2O fluxes from conventional agriculture treatment plots exceeding fluxes from tilled and untilled mid-successional plots. Site preference for soil-derived N2O was between 19.0 and 21.8 ‰ from the conventional agriculture treatment plots.
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