Disentangling gross N2O production and consumption in soil.

Yuan Wen,Georg Willibald,Klaus Butterbach-Bahl,Ralf Kiese,Benjamin Wolf,Andrea Carminati,Edzo Veldkamp,Michael Dannenmann,Zhe Chen,Marife D Corre

doi:10.1038/srep36517

Yuan Wen, Georg Willibald + Show 8 more

Open Access

https://doi.org/10.1038/srep36517

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Abstract

The difficulty of measuring gross N2O production and consumption in soil impedes our ability to predict N2O dynamics across the soil-atmosphere interface. Our study aimed to disentangle these processes by comparing measurements from gas-flow soil core (GFSC) and 15N2O pool dilution (15N2OPD) methods. GFSC directly measures soil N2O and N2 fluxes, with their sum as the gross N2O production, whereas 15N2OPD involves addition of 15N2O 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 N2O production and consumption measured by 15N2OPD were only 10% and 6%, respectively, of those measured by GFSC. However, 15N2OPD remains the only method that can be used under field conditions to measure atmospheric N2O uptake in soil. We propose to use different terminologies for the gross N2O fluxes that these two methods quantified. For 15N2OPD, we suggest using ‘gross N2O emission and uptake’, which encompass gas exchange within the 15N2O-labelled, soil air-filled pores. For GFSC, ‘gross N2O production and consumption’ can be used, which includes both N2O emitted into the soil air-filled pores and N2O directly consumed, forming N2, in soil anaerobic microsites.

Highlights

The difficulty of measuring gross N2O production and consumption in soil impedes our ability to predict N2O dynamics across the soil-atmosphere interface
Cropland and beech forest, net N2O emissions accounted for 66–79% of gross N2O production (Fig. 1d)
Net N2O fluxes accounted, on average, for only 24% of gross N2O production (Fig. 1d), and most (76%) of the produced N2O was further reduced to N2

Summary

Introduction

The difficulty of measuring gross N2O production and consumption in soil impedes our ability to predict N2O dynamics across the soil-atmosphere interface. Our study aimed to disentangle these processes by comparing measurements from gas-flow soil core (GFSC) and 15N2O pool dilution (15N2OPD) methods. GFSC directly measures soil N2O and N2 fluxes, with their sum as the gross N2O production, whereas 15N2OPD involves addition of 15N2O into a chamber headspace and measuring its isotopic dilution over time. 15N2OPD remains the only method that can be used under field conditions to measure atmospheric N2O uptake in soil. For GFSC, ‘gross N2O production and consumption’ can be used, which includes both N2O emitted into the soil air-filled pores and N2O directly consumed, forming N2, in soil anaerobic microsites. It is generally known that microbial nitrification and denitrification in soils are the major sources of atmospheric N2O, it remains a struggle to disentangle and quantify gross rates of microbial N2O production and consumption in soil which, in turn, determine the net N2O flux across the soil-atmosphere interface. Soil N2O consumption, is often ignored because it is prone to be masked by the much larger N2O production[4] and is difficult to measure directly (e.g. as soil N2 flux) against a very high (78%) atmospheric background[9]

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Conclusion