Mycorrhiza-mediated recruitment of complete denitrifying Pseudomonas reduces N2O emissions from soil

Summary

This mechanistic study demonstrates that arbuscular mycorrhizal fungal hyphae selectively enrich N₂O-reducing Pseudomonas bacteria in soil microsites, with carboxylate exudates functioning as both chemotactic attractants and triggers for nosZ gene expression. Laboratory characterisation of P. fluorescens strain JL1 and an 11-year field experiment confirm that this AMF–bacteria cooperation significantly reduces denitrification-derived N₂O emissions in carbon- and nitrogen-rich residue patches. The findings provide molecular evidence for how natural soil microbiological mechanisms can mitigate agricultural greenhouse gas emissions.

Regional applicability

The mechanisms identified are likely relevant to UK soils where AMF are naturally present, but the study's focus on high C and N residue patches in what appear to be higher-productivity systems may require validation under UK temperate conditions, crop rotations, and residue management practices. The approach offers potential for UK farms seeking to reduce N₂O emissions through biological rather than chemical interventions.

Key measures

N₂O emission reductions (maximum 63%); abundance and expression of clade I nosZ, nirS, and nirK genes via amplicon and shotgun metagenomic sequencing; chemotaxis and nosZ upregulation of P. fluorescens strain JL1 in response to carboxylate exudates; hyphal length density and correlation with nosZ gene abundance over 11 years

Outcomes reported

The study measured N₂O emissions from soil residue patches under AMF colonisation, quantified the abundance and expression of denitrification genes (nosZ, nirS, nirK), and characterised the chemotactic and gene expression responses of N₂O-reducing Pseudomonas bacteria to hyphal exudates. An 11-year field experiment validated the relationship between hyphal length density and clade I nosZ gene abundance.

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