Nina Roothans et al.(2024) combined long-term, metagenomically resolved metaproteomics and ex situ kinetic characterizations to elucidate the ecophysiology of an N2O-emitting wastewater treatment plant community. The integration of these data enabled the identification of a cascade of environmental and operational triggers that induce metabolic nitrification imbalance, leading to N2O emissions. Correspondence to: m.laureni@tudelft.nl (Michele Laureni, TUD).