Abstract
Artificial light pollution is increasing worldwide with pervasive effects on ecosystem structure and function, yet its influence on ecosystem metabolism remains largely unknown. Here we combine artificial light at night (ALAN) intensity metrics with eddy covariance observations across 86 sites in North America and Europe to show that ALAN indirectly decreases annual net ecosystem exchange by enhancing ecosystem respiration (R (e)). At half-hourly and daily scales, we detect consistent nonlinear interactions between ALAN and night duration, with R (e) increasing under higher ALAN and partially decoupling from gross primary production. At the annual scale, gross primary production shows no direct ALAN response and is instead influenced by the growing season length and urban proximity, whereas R (e) responds more strongly and consistently across timescales. Our findings show that ALAN disrupts the fundamental energetic constraints on ecosystem metabolism, warranting the inclusion of light pollution in global change and carbon-climate feedback assessments.