Quantifying thermal adaptation of cropland N2O emissions and its compensatory microbial basis

Quantifying the response of cropland N2O emissions to future warming is critical for predicting the feedback between nitrogen cycling and climate change. A central uncertainty is whether soil N2O emissions thermally adapts, an assumption often invoked in carbon-cycle theory. If present, both the magnitude and mechanistic basis of this adaptation remain unresolved. Here, using a global compilation of N₂O flux measurements from temperature-controlled incubations of cropland soils, we identify mean annual temperature (MAT) as the dominant predictor of N2O fluxes and their temperature sensitivity (Q₁₀). Along the MAT gradient, N2O fluxes at a reference temperature (25 ℃) declined by 12.2 ± 2.6% (mean ± SE) per °C, and Q₁₀ decreased by 0.05 ± 0.01 per °C. To probe mechanisms, we conducted two complementary experiments using soil samples spanning climate gradients: a short-term temperature-response assay and a 90-day warming incubation, both under controlled moisture and with 15N-labelled substrate additions. Across both datasets, warmer thermal regimes (higher MAT and experimental warming) reconfigured temperature response curves toward lower Q10 and higher Topt (temperature optima) for both nitrification and denitrification. Mechanistically, this pattern is aligning with the compensatory theory, microbial N2O production rates normalized to mean nitrifier and denitrifier RNA abundances were reduced under warmer thermal regimes. Together, these findings highlighted that soil N₂O production adapts to local thermal regimes across space and to sustained warming through time, implying that future warming may amplify cropland N₂O emissions, but less than commonly predicted.