Disentangling gross N(2)O production and consumption in soil

The difficulty of measuring gross N(2)O production and consumption in soil impedes our ability to predict N(2)O dynamics across the soil-atmosphere interface. Our study aimed to disentangle these processes by comparing measurements from gas-flow soil core (GFSC) and (15)N(2)O pool dilution ((15)N(2)OPD) methods. GFSC directly measures soil N(2)O and N(2) fluxes, with their sum as the gross N(2)O production, whereas (15)N(2)OPD involves addition of (15)N(2)O into a chamber headspace and measuring its isotopic dilution over time. Measurements were conducted on intact soil cores from grassland, cropland, beech and pine forests. Across sites, gross N(2)O production and consumption measured by (15)N(2)OPD were only 10% and 6%, respectively, of those measured by GFSC. However, (15)N(2)OPD remains the only method that can be used under field conditions to measure atmospheric N(2)O uptake in soil. We propose to use different terminologies for the gross N(2)O fluxes that these two methods quantified. For (15)N(2)OPD, we suggest using ‘gross N(2)O emission and uptake’, which encompass gas exchange within the (15)N(2)O-labelled, soil air-filled pores. For GFSC, ‘gross N(2)O production and consumption’ can be used, which includes both N(2)O emitted into the soil air-filled pores and N(2)O directly consumed, forming N(2), in soil anaerobic microsites.