Elevated CO 2 and O 3 modify N turnover rates, but not N 2O emissions in a soybean agroecosystem

Charlotte Decock, Haegeun Chung, Rodney Venterea, Sharon B. Gray, Andrew D.B. Leakey, Johan Six

Research output: Contribution to journalArticlepeer-review

Abstract

In order to predict and mitigate future climate change, it is essential to understand plant-mediated effects of elevated CO 2 (eCO 2) and O 3 (eO 3) on N-cycling, including N 2O emissions. This is of particular interest for agroecosystems, since N-cycling and N 2O emissions are responsive to adaptive management. We investigated the interaction of soil moisture content with eCO 2 and eO 3 on potential N 2O emissions from SoyFACE during a 28-day laboratory incubation experiment. We also assessed field N 2O 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 (δ 15N). This method relies on the concept that soil δ 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 eCO 2 and eO 3 on laboratory and field measured N 2O 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 eCO 2, 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 eO 3, leading to increased gaseous N loss, most likely in the form of N 2. Given that effects of eCO 2 and eO 3 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 eCO 2 decelerates whereas eO 3 accelerates N-cycling in the longer-term, but feedback through changed N 2O emissions is not occurring in this soybean system.

Original languageEnglish (US)
Pages (from-to)104-114
Number of pages11
JournalSoil Biology and Biochemistry
Volume51
DOIs
StatePublished - Aug 2012

Keywords

  • Agroecosystem
  • Climate change
  • Greenhouse gases
  • N-budget
  • Natural abundance stable isotopes
  • Nitrous oxide
  • Soybean

ASJC Scopus subject areas

  • Microbiology
  • Soil Science

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