Soil moisture and the number of simultaneous stressors drive interactions among global changes on denitrification

Denitrification, the microbial reduction of nitrate into nitrogen-containing gases, is a major source of nitrous oxide (N₂O), a potent greenhouse gas. How denitrification responds to the concurrent influence of multiple global changes remains uncertain. Here, we investigate the interactive effects of warming, elevated CO₂, increased precipitation, nitrogen supply and fire on potential denitrification in a long-term global change experiment. We show that the combined effects of global changes deviate from expectations based on combining their effects as single factors. Wetter soils promoted positive interaction terms (i.e., observed combined effects that are greater than expected combined effects), and the strength of those interactions increased linearly with the number of simultaneous global changes. In a world of increased precipitation in many areas and of multifactor global change, our findings suggest that current models underestimate the impacts of global change on denitrification and associated climate feedbacks.