Arbuscular mycorrhizal fungi markedly reduce N2O emissions from an organic soil

Background/Question/Methods

Arbuscular mycorrhizal fungi (AMF) form symbiotic associations with over 80% of terrestrial plants. Recent studies showed that AMF can enhance plant N uptake and consequently alter N₂O emissions. They may reduce N₂O emissions through reducing soil NO₃- for denitrification or increase N₂O emissions through supplying labile C for denitrifying microbes. However, few experiments have so far assessed the relative effect of AMF removal of N and AMF supply of labile C. We conducted a microcosm experiment to assess the effect of AMF on N₂O emissions in two soils with different sources and quantity of N inputs. We employed a nylon mesh (20 um) to allow AMF hyphae but not fine roots to penetrate through so that AMF effects can be quantified.

Results/Conclusions

AMF significantly reduced N₂O emissions by 25% and 44% in an organic soil with low and high organic N inputs, respectively. In contrast, AMF had only marginal or no effect on N₂O emissions in the conventional soil with synthetic N (urea) inputs. Also, AMF did not stimulate N₂O emissions in spite of high NO₃- in soil, indicating that the effect of AMF through C supply to denitrifying microbes was negligible. Together, our results suggest that AMF removal of mineral N (likely NH₄⁺) dominates their effects on N₂O emissions.