308-6 Soil Nitrogen Transformations Under Elevated CO2 and O3 Concentrations During the Soybean Growing Season.

See more from this Division: S03 Soil Biology & Biochemistry
See more from this Session: Soil Carbon, Nitrogen and GHG Fluxes: I
Wednesday, November 3, 2010: 9:45 AM
Long Beach Convention Center, Room 104A, First Floor
Share |

Engil Pereira1, Haegeun Chung2, Kate Scow3, Michael Sadowsky4, Chris van Kessel1 and Johan Six5, (1)University of California, Davis, Davis, CA
(2)Division of Environmental Science and Ecological Engineering, Korea University, Seoul, South Korea
(3)1 Shields Avenue, University of California-Davis, Davis, CA
(4)University of Minnesota, St. Paul, MN
(5)Department of Plant Sciences, University of California, Davis, CA

The increasing atmospheric concentrations of CO2 and O3 are likely to alter ecosystem functioning by modifying rates of plant photosynthesis and production of plant biomass. Soil microorganisms are driven by the amount and quality of plant organic material and conduct crucial ecosystem processes, such as N cycling. This study aims to investigate how soil N cycling will respond to elevated CO2 and O3. More specifically, it focuses on the changes in nitrifiers and denitrifiers communities, as well as N transformation processes, under elevated CO2 and O3 conditions within the growing season and across soil environments (i.e., rhizosphere and bulk soil) in a soybean (Glycine max (L.) Merr.) agroecosystem. Soil samples were collected at different phenological stages of the soybean plants: fourth trifoliolate leaf (V4), full pod (R4), and full maturity (R8) during the 2008 growing season at the SoyFACE experiment in Champaign-Urbana, Illinois. Elevated CO2 increased 16S rRNA gene abundance during R8 compared to V4 and R4. Neither elevated CO2 nor O3 had significant effects on amoA abundance.  The nosZ gene abundance was significantly more abundant in the rhizosphere compared to the bulk soil. Although not statistically significant, elevated O3 tended to increase the abundance of nosZ, whereas elevated CO2 did not change nosZ abundance. Although total soil N was significantly higher under elevated than ambient O3 conditions, elevated O3 decreased soil mineral N through a reduction in plant material input and increased denitrification, which was indicated by the higher abundance of nosZ. Elevated CO2 did not alter any of the parameters evaluated and elevated CO2 and O3 showed no interactive effects on nitrifier and denitrifier communities nor on the concentration of total and mineral N in soil. This study shows that elevated CO2 may have limited effects on terrestrial N transformations in soybean agroecosystems, but elevated O3 can lead to a decrease in plant N availability in both the rhizosphere and bulk soil. In conclusion, in addition to reducing photosynthetic rates, elevated O3 can also affect ecosystem productivity by reducing the mineralization rates of plant-derived residues.  

See more from this Division: S03 Soil Biology & Biochemistry
See more from this Session: Soil Carbon, Nitrogen and GHG Fluxes: I