REGULAR ARTICLE Effects of elevated CO 2 and O 3 on N-cycling and N 2 O emissions: a short-term laboratory assessment Charlotte Decock & Johan Six Received: 4 March 2011 /Accepted: 12 August 2011 /Published online: 10 September 2011 # Springer Science+Business Media B.V. 2011 Abstract Background and aims Elevated atmospheric CO 2 (eCO 2 ) and tropospheric O 3 (eO 3 ) can alter soil microbial processes, including those underlying N 2 O emissions, as an indirect result of changes in plant inputs. In this study, effects of eCO 2 and eO 3 on sources of N 2 O in a soybean (Glycine max (L.) Merr.) agroecosystem in Illinois (SoyFACE) were investigated. We hypothesized that increases in available C and anaerobic microhabitat under eCO 2 would stimulate N 2 O emissions, with a proportionally larger increase in denitrification derived N 2 O (N 2 O D ) compared to nitrification plus nitrifier denitrification derived N 2 O (N 2 O N+ND ). We expected opposite effects under eO 3 . Methods Isotopically labeled 15 NH 4 14 NO 3 and 14 NH 4 15 NO 3 were used to evaluate mineral N trans- formations, N 2 O D , and N 2 O N+ND in a 12-day incubation experiment. Results We observed minimal effects of eCO 2 and eO 3 on N 2 O emissions, movement of 15 N through mineral N pools, soil moisture content and C availability. Possibly, altered C and N inputs by eCO 2 and eO 3 were small relative to the high soil organic C content and N-inputs via biological N 2 - fixation, minimizing potential effects of eCO 2 and eO 3 on N-cycling. Conclusion We conclude that eCO 2 and eO 3 did not affect N 2 O emissions in the short term. However, it remains to be tested whether N 2 O emissions in SoyFACE will be unaltered by eCO 2 and eO 3 on a larger temporal scale under field conditions. Keywords Elevated CO 2 . Eelevated ozone . Nitrous oxide . N-cycle . 15 N tracer . Agroecosystem Abbreviations eCO 2 elevated carbon dioxide eO 3 elevated ozone N 2 O total total nitrous oxide N 2 O D denitritrification derived nitrous oxide N 2 O N+ND nitrification plus nitrifier denitrification derived nitrous oxide WFPS water filled pore space Introduction Since the start of the industrial revolution, fossil fuel combustion and land use change have caused a drastic increase in the concentration of atmospheric carbon dioxide (CO 2 ) (IPCC 2007). In the meantime, anthropogenic activities have promoted the formation of tropospheric ozone (O 3 ) through photochemical processes from various precursors (carbon monoxide, Plant Soil (2012) 351:277–292 DOI 10.1007/s11104-011-0961-1 Responsible Editor: Elizabeth M. Baggs. C. Decock (*) : J. Six Department of Plant Sciences, University of California, One Shields Ave., Davis, CA 95616, USA e-mail: cldecock@ucdavis.edu