Dominant role of water-extractable soil chemicals in modulating N₂O emissions relative to soil bacteriome

Soil nitrous oxide (N₂O) emissions are influenced both by soil chemical properties and microbiome composition; however, their relative contributions remain unclear. We used soil-water extracts (SW), and cell extracts (bacteriomes) from two contrasting soils, black soil (BS) and fluvo-aquic soil (FS), to evaluate how water-extractable soil chemicals and bacteriomes directly impact N₂O emissions, as well as how SW influences bacteriome composition. Results show that SW chemistry, particularly pH, plays a dominant role in regulating denitrification dynamics, while bacteriome effects are less significant. In native BS water extract (BSW, pH 6.5), cell extract from BS (BB bacteriomes) exhibited high N₂O emissions (N₂O index = 0.669), but their denitrification efficiency improved in FS water extract (FSW, pH 8.2), reducing the N₂O index to 0.0491. Conversely, cell extract from FS (FB bacteriomes) in native FSW (pH 8.2) demonstrated efficient denitrification (N₂O index = 0.006), but exposure to BSW increased N₂O emissions (∼ 100 µmol vial⁻¹, N₂O index = 0.295). Bacterial community analysis revealed that high pH fostered diverse denitrifiers, including napA-harboring Pseudoxanthomonas and Lysobacter, and nosZ Clade II Chitinophaga, which are linked to N₂O reduction. In contrast, low pH favored narG-harboring incomplete denitrifiers like Klebsiella and Enterobacter. In the BB bacteriome, BSW promoted Rhodanobacter, which hindered complete denitrification, while FSW enriched complete denitrifiers like Cupriavidus and Ensifer. Conversely, BSW negatively impacted the enrichment of complete denitrifier Acidovorax in the FB bacteriome. This study contributes to the growing evidence of the critical roles of soil physicochemical properties and bacteriome composition in determining N₂O fluxes from agricultural soils.