Elevated CO2 and O3 modify N turnover rates, but not N2O emissions in a soybean agroecosystem

• Published in: Soil biology & biochemistry Vol. 51; pp. 104 - 114
• Main Authors: Decock, Charlotte, Chung, Haegeun, Venterea, Rodney, Gray, Sharon B., Leakey, Andrew D.B., Six, Johan
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.08.2012
• Subjects: Agroecosystem; Climate change; Greenhouse gases; N-budget; Natural abundance stable isotopes; Nitrous oxide; Soybean; Climate change; Nitrous oxide; N-budget; Soybean; Greenhouse gases; Natural abundance stable isotopes; Agroecosystem
• ISSN: 0038-0717; 1879-3428
• DOI: 10.1016/j.soilbio.2012.04.015

In order to predict and mitigate future climate change, it is essential to understand plant-mediated effects of elevated CO2 (eCO2) and O3 (eO3) on N-cycling, including N2O emissions. This is of particular interest for agroecosystems, since N-cycling and N2O emissions are responsive to adaptive management. We investigated the interaction of soil moisture content with eCO2 and eO3 on potential N2O emissions from SoyFACE during a 28-day laboratory incubation experiment. We also assessed field N2O fluxes during 2 soybean-growing seasons. In addition, we sought to link previously observed changes in soybean growth and production to belowground processes over a longer time scale by analyzing changes in natural abundance stable isotope ratios of soil N (δ15N). This method relies on the concept that soil δ15N can only change when inputs or outputs with an isotope signature different from that of soil N are altered. We found no major effects of eCO2 and eO3 on laboratory and field measured N2O emissions. Natural abundance isotope analyses suggested, however, a decrease in belowground allocation of biologically fixed N in combination with decreased total gaseous N loss by eCO2, resulting in a tighter N cycle in the longer-term. In contrast, the isotope data suggested an increase in belowground allocation of biologically fixed N under eO3, leading to increased gaseous N loss, most likely in the form of N2. Given that effects of eCO2 and eO3 on N pools and instantaneous transformation rates in surface soil layers of this agroecosystem have been minimal, our results illustrate the importance of evaluating longer-term changes in N turnover rates. We conclude that eCO2 decelerates whereas eO3 accelerates N-cycling in the longer-term, but feedback through changed N2O emissions is not occurring in this soybean system. ► Elevated CO2 and O3 did not affect N2O fluxes from a soybean agroecosystem. ► There was no interaction between soil moisture and elevated CO2 or O3 on N2O. ► Natural abundance 15N of soil N suggested longer-term changes in N-cycling. ► Elevated CO2 accelerated N-cycling, and elevated O3 decelerated N-cycling.