Effect of nitrogen deposition on centennial forest water-use efficiency

Abstract The uptake of carbon dioxide (CO 2 ) from the atmosphere through photosynthesis is accompanied by an inevitable loss water vapor stomata leaves. rate leaf-level CO assimilation per unit stomatal conductance, i.e. intrinsic water-use efficiency (WUE i ), thus a key characteristic terrestrial ecosystem functioning that central to global hydroclimate system. Empirical evidence and theory suggest positive response forest WUE increased levels globally. Although exists for effect nitrogen (N) inputs on , it not clear how trends in atmospheric N deposition have affected past. Here we combine twentieth-century climate with stable isotope signature tree rings document trend reversal at two sites Switzerland, matches timing deposition. Using generalized additive models (GAMs), fitted observed time series multiple environmental covariates. This suggested significant long-term site was exposed higher levels. ratio increase (dWUE /dCO declined 96% after 1980 (from 0.53 0.02) beech 72% spruce 0.46 0.13) concurrent sharp decline GAM model scenarios, show had 1980s, would more strongly increasing . limited 1950–1980 decades signals improvements air quality across Europe, role pollution must be reconsidered interpretation ring studies building proxies are pivotal understanding future sink capacity ecosystems change.