Effects of arbuscular mycorrhizal fungi on N2O emission under elevated CO2
Nitrous oxide (N2O) is a potent greenhouse gas that significantly contribute to global warming. Elevated CO2 often increases soil N2O emissions, but the underlying mechanisms are not fully understood (van Groenigen et al. 2011).
Arbuscular mycorrhizal fungi (AMF) form symbiotic associations with over 80% of terrestrial plants and affects N cycling through enhancing plant N acquisition. Consequently, AMF may decrease soil N2O emissions by reducing soil NO3- for denitrification or increase N2O emissions through supplying labile C for denitrifying microbes (Bender et al. 2014; Storer 2013).
However, to our knowledge, no experiments have so far assessed the relative effects of AMF removal of N and AMF supply of labile C on soil N2O emissions under elevated CO2.
We conducted a microcosm experiment to assess the AMF effects on N2O emissions under elevated CO2 with two different sources of N inputs using hyphal compartment technique. The objectives of this study were to: (1) examine the role of AMF in N2O emissions under elevated CO2, and (2) determine the effects of nitrogen species (NH4+-N or NO3- -N) on N2O emissions. The findings from this study would advance our understanding of the mechanisms of enhanced soil N2O emissions under elevated CO2.
N2O emissions were significantly higher under elevated than ambient CO2 when NO3- -N was applied. In contrast, NH4+-N did not have any stimulatory effect on N2O emissions, suggesting that CO2-inhibition of plant NO3--N utilization may have stimulated denitrification. AMF significantly reduced soil N2O emission and did not enhance N2O emissions in spite of high NO3--N in soil.