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 T_opt (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.