Large losses of ammonium-nitrogen from a rice ecosystem under elevated CO2

Inputs of nitrogen into terrestrial ecosystems, mainly via the use of
ammonium-based fertilizers in agroecosystems, are enormous, but its fate
under elevated atmospheric carbon dioxide (CO2) is not well understood. We
have taken advantage of a 15-year free air CO2 enrichment study to
investigate the influence of elevated CO2 on the transformation of
ammonium-nitrogen in a rice ecosystem in which ammonium is usually assumed
to be stable under anaerobic conditions. We demonstrate that elevated CO2
causes substantial losses of ammonium-nitrogen that result from anaerobic
oxidation of ammonium coupled to reduction of iron. We identify a new,
autotrophic member of the bacterial order Burkholderiales that may use
soil CO2 as a carbon source to couple anaerobic ammonium oxidation and
iron reduction. These findings offer insight into the coupled cycles of
nitrogen and iron in terrestrial ecosystems and raise questions about the
loss of ammonium-nitrogen from arable soils under future climate-change
scenarios.