Effects of arbuscular mycorrhizal fungi on N2O emission under elevated CO2

Background/Question/Methods

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.

Results/Conclusions

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.