@article{wu_chen_tu_qiu_burkey_reberg-horton_peng_hu_2017, title={CO2-induced alterations in plant nitrate utilization and root exudation stimulate N2O emissions}, volume={106}, ISSN={["0038-0717"]}, DOI={10.1016/j.soilbio.2016.11.018}, abstractNote={Atmospheric carbon dioxide enrichment (eCO2) often increases soil nitrous oxide (N2O) emissions, which has been largely attributed to increased denitrification induced by CO2-enhancement of soil labile C and moisture. However, the origin of the N remains unexplained. Emerging evidence suggests that eCO2 alters plant N preference in favor of ammonium (NH4+-N) over nitrate (NO3−-N). Yet, whether and how this attributes to the enhancement of N2O emissions has not been investigated. We conducted a microcosm experiment with wheat (Triticum aestivum L.) and tall fescue (Schedonorus arundinaceus (Schreb.) Dumort.) to examine the effects of eCO2 on soil N2O emissions in the presence of two N forms (NH4+-N or NO3−-N). Results obtained showed that N forms dominated eCO2 effects on plant and microbial N utilization, and thus soil N2O emissions. Elevated CO2 significantly increased the rate and the sum of N2O emissions by three to four folds when NO3−-N, but not NH4+-N, was supplied under both wheat and tall fescue. While enhanced N2O emission was more related to the reduced plant NO3−-N uptake under wheat, it concurred with increased labile C under tall fescue. In the presence of NO3−-N, significantly lower shoot biomass N and 15N, but higher plant biomass C:N ratio, microbial biomass C and N, and/or soil extractable C indicated that eCO2 constrained plant NO3−-N utilization and likely stimulated root exudation. We propose a new conceptual model in which eCO2-inhibition of plant NO3−-N uptake and/or CO2-enhancement of soil labile C enhances the N and/or C availability for denitrifiers and increases the intensity and/or the duration of N2O emissions. Together, these findings indicate that CO2-enhancement of soil N and labile C favors denitrification, suggesting that management of N fertilizers in intensive systems will likely become more challenging under future CO2 scenarios.}, journal={SOIL BIOLOGY & BIOCHEMISTRY}, author={Wu, Keke and Chen, Dima and Tu, Cong and Qiu, Yunpeng and Burkey, Kent O. and Reberg-Horton, S. Chris and Peng, Shaolin and Hu, Shuijin}, year={2017}, month={Mar}, pages={9–17} }