Microdialysis reveals limits of tannin-mediated nitrous oxide mitigation in slurry-amended soil

Abstract

Nitrous oxide (N₂O) emissions following slurry application are highly variable, partly as slurry creates localized soil hotspots where microbial activity and oxygen availability strongly constrain nitrogen cycling. Phenolic compounds released by plant roots have been proposed as biological nitrification inhibitors, but their effectiveness within slurry hotspots remains unknown. Here, we used medical microdialysis to deliver methyl gallate (MG), a simple galloyl ester and structural constituent of hydrolyzable tannins, directly into a defined slurry microsite to test whether biochemical regulation could mitigate N₂O production at the scale where emissions originate. Slurry addition strongly increased CO₂, CH₄, and N₂O emissions, indicating intense microbial activity and oxygen-limited conditions consistent with denitrification dominance. MG did not significantly affect cumulative emissions of N₂O, CO₂, or CH₄. The results suggest that denitrification driven by carbon-induced oxygen depletion may have limited the detectability of any potential effects of MG on nitrification, although limited intrinsic effectiveness of MG under these conditions cannot be excluded.

Core Ideas

• Slurry creates oxygen-limited N₂O-producing soil microsites.
• Microdialysis enables targeted solute delivery to slurry bands.
• Methyl gallate did not reduce N₂O emissions in slurry hotspots.
• Carbon-driven oxygen depletion likely dominated N₂O production.