Articles | Volume 13, issue 5
https://doi.org/10.5194/bg-13-1705-2016
https://doi.org/10.5194/bg-13-1705-2016
Research article
 | 
18 Mar 2016
Research article |  | 18 Mar 2016

Net soil–atmosphere fluxes mask patterns in gross production and consumption of nitrous oxide and methane in a managed ecosystem

Wendy H. Yang and Whendee L. Silver

Abstract. Nitrous oxide (N2O) and methane (CH4) are potent greenhouse gases that are both produced and consumed in soil. Production and consumption of these gases are driven by different processes, making it difficult to infer their controls when measuring only net fluxes. We used the trace gas pool dilution technique to simultaneously measure gross fluxes of N2O and CH4 throughout the growing season in a cornfield in northern California, USA. Net N2O fluxes ranged 0–4.5 mg N m−2 d−1 with the N2O yield averaging 0.68 ± 0.02. Gross N2O production was best predicted by net nitrogen (N) mineralization, soil moisture, and soil temperature (R2 = 0.60, n = 39, p< 0.001). Gross N2O reduction was correlated with the combination of gross N2O production rates, net N mineralization rates, and CO2 emissions (R2 = 0.74, n = 39, p< 0.001). Overall, net CH4 fluxes averaged −0.03 ± 0.02 mg C m−2 d−1. The methanogenic fraction of carbon mineralization ranged from 0 to 0.27 % and explained 40 % of the variability in gross CH4 production rates (n = 37, p< 0.001). Gross CH4 oxidation exhibited a strong positive relationship with gross CH4 production rates (R2 = 0.67, n = 37, p< 0.001), which reached as high as 5.4 mg C m−2 d−1. Our study is the first to demonstrate the simultaneous in situ measurement of gross N2O and CH4 fluxes, and results highlight that net soil–atmosphere fluxes can mask significant gross production and consumption of these trace gases.

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Short summary
Nitrous oxide and methane are potent greenhouse gases that are both produced and consumed in soil. Using stable isotope tracers, we found that 68 % of nitrous oxide produced in soil was emitted to the atmosphere throughout the growing season in a cornfield despite variable soil conditions. Gross methane production and consumption were tightly coupled, resulting in near-zero net fluxes. Our results challenge our understanding of controls on nitrous oxide and methane dynamics in upland soils.
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