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Elevated CO2 and O3 modify N turnover rates, but not N2O emissions

Author:
Decock, Charlotte, Chung, Haegeun, Venterea, Rodney, Gray, Sharon B., Leakey, Andrew D.B., Six, Johan
Source:
Soil biology & biochemistry 2012 v.51 pp. 104
ISSN:
0038-0717
Subject:
agroecosystems, carbon dioxide, climate change, crop production, emissions, nitrogen content, nitrous oxide, soil surface layers, soil water content, soybeans, stable isotopes
Abstract:
In order to predict and mitigate future climate change, it is essential to understand effects of elevated CO2 (eCO2) and O3 (eO3) on N-cycling, including N2O emissions, due to plant mediated changes. 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 (delta 15N). This method relies on the concept that soil delta 15N 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 N2O emissions. Natural abundance isotope analyses suggested 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. Under eO3, increased belowground allocation of biologically fixed N led 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 previously observed for this agroecosystem have been minimal, our results illustrate the importance of tools that can detect 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 soybean systems.
Agid:
59581
Handle:
10113/59581