Field Warming-Based Observations Reveal Constrained Apparent Temperature Sensitivities of Cropland N2O Emissions

Abstract

The response of nitrous oxide (N₂O) emissions to warming is critical for accurately projecting nitrogen-climate feedback. Compelling evidences have shown that N₂O emissions are temperature dependent, offering insights into their intrinsic temperature sensitivity. However, when extrapolating from laboratory-controlled to field-ambient conditions, it remains unclear how this temperature sensitivity varied across cropland fields subject to diverse environmental and anthropogenic constraints. We performed a comprehensive meta-analysis of 144 field-warming observations worldwide, aiming to address the magnitude, heterogeneity, and drivers of such apparent temperature sensitivity. The results showed that mean growing-season field-scale N₂O emissions were not strongly temperature dependent with low averaged activation energy (0.32 eV) compared with that of laboratory-scale observations (0.62 eV). At site levels, the spatial variation in such temperature sensitivity was primarily driven by the interactions of nitrogen fertilization, edaphic, and climatic variables. This analysis also identified a crucial yet frequently overlooked role of soil pH in nonlinearly modulating such temperature sensitivity. Our findings provide evidence for understanding nitrogen and climate feedback by capturing the soil-climate-management constrained warming response and highlight the importance of incorporating these constraints into models to improve prediction accuracy.