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Title:   Author  item
                                            DECOCK, CHARLOTTE - University Of Californiaitem
                                            CHUNG, HAEGEUN - University Of Californiaitem
                                            Venterea, Rodney

                                                         - *Rod*item
                                            SIX, JOHAN - University Of California
  Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
                                    Publication Type: Abstract Only
                                    Publication Acceptance Date: 5/1/2010
                                    Publication  Date: 10/31/2010
                                    Citation: Decock, C., Chung, H., Venterea, R.T., Six, J. 2010. The Effect of Elevated CO2 and O3 on Soil Nitrogen Inputs and Losses in a Soybean Agroecosystem in Illinois [abstract]. ASA-CSSA-SSSA Annual Meeting Abstracts. Paper No. 592.Interpretive Summary:
                                Technical Abstract: It has been found that elevated atmospheric carbon dioxide (eCO2) and tropospheric ozone (eO3) affect belowground microbial processes, including N transformations, through plant-mediated changes. Conversely, changes in soil organic carbon sequestration and plant biomass production are constrained by N availability. Furthermore, changes in N losses to the groundwater or the atmosphere cause eutrophication of aquatic ecosystems and global climate change, respectively. Therefore, it is pertinent to assess the effect of eCO2 and eO3 on N inputs and losses. In a soybean agroecosystem in Illinois, we used natural abundance stable isotopes as a proxy to integrate long-term N inputs and losses, based on minimal isotopic discrimination during biological N2-fixation, and 15N depletion associated with lost N. Our isotopic model suggested that N-inputs and losses decreased by eCO2, whereas inputs and losses increased by eO3. Under eCO2, changes in inputs and losses balanced each other out, while a larger increase in inputs compared to losses under eO3 resulted in a larger soil N content under eO3 compared to ambient. Differences in N-losses between treatments are due to removal of soil derived N by harvest, N leaching and gaseous N emissions. Soil derived N removed by harvest was increased by eCO2, and there was a stimulation of the cumulative N2O flux during the growing season in 2005 but not in 2006. Consequently, the reduction in N loss under eCO2 compared to ambient must be a result of decreased N leaching or decreased total gaseous loss. eO3 did not affect the amount of soil N removed by harvest or the cumulative N2O flux during the growing season. Hence, the increased N loss under eO3 compared to ambient might be due to changes in total gaseous N loss, N2O emissions during the non-growing season or increased leaching. In conclusion, our results warn for increased environmental risk for hazardous N loss from agroecosystems under changing atmospheric conditions.


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