Summary
This study demonstrates that arbuscular mycorrhizal fungi (AMF) reduce denitrification-derived N2O emissions from nitrogen-rich soil residue patches by selectively enriching and recruiting complete denitrifying Pseudomonas fluorescens strains on their hyphae. The mechanism involves AMF hyphal exudates—particularly carboxylates—acting as chemotactic attractants and transcriptional triggers that upregulate nosZ gene expression in these bacteria, thereby enhancing their capacity to reduce N2O to inert N2. Findings were validated through laboratory phenotypic characterisation, inoculation experiments, and an 11-year field study showing a positive correlation between hyphal density and clade I nosZ abundance.
UK applicability
The findings are potentially relevant to UK agriculture, particularly in systems with high organic matter inputs and residue patches where N2O emissions are problematic. However, the study did not report data specific to UK soil types, climate, or cropping systems, so applicability would require validation under British conditions with locally relevant AMF communities and crop residues.
Key measures
N2O emission reduction (maximum 63%), clade I nosZ gene abundance and expression, relative abundance of nirS and nirK genes, hyphal length density, nosZ gene expression in isolated P. fluorescens strain JL1, correlation between hyphal length density and nosZ abundance over 11 years
Outcomes reported
The study measured N2O emissions from soil residue patches and the abundance and expression of denitrification-related genes (nosZ, nirS, nirK) in response to arbuscular mycorrhizal fungal colonisation. It quantified the chemotactic response and nosZ gene expression of isolated N2O-reducing Pseudomonas fluorescens to hyphal exudates.
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