Growth and assemblage dynamics of temperate forest tree species match physiological resilience to changes in atmospheric chemistry

Human-induced environmental changes are altering productivity and species composition in forests, significantly impacting tree physiology, growth, water uptake, and nutrient acquisition. Investigating the intricate interplay between plant physiology and environmental shifts, we analyzed tree-ring isotopes (δ13C, δ18O, and δ15N) to track long-term trends in intrinsic water-use efficiency (iWUE) and nitrogen availability for European beech, Norway spruce, and silver fir in an old-growth temperate mountain forest since 1501 CE. Our findings reveal that Norway spruce has experienced iWUE saturation, exacerbated by acidic precipitation, resulting in growth declines during periods of high acidic air pollution and increased drought frequency. Conversely, the deep-rooted European beech shows physiological resilience to acid deposition and benefits from higher nitrogen deposition and air temperatures, maintaining climatically unrestricted stem growth. Silver fir demonstrates the most dynamic response to acidic air pollution, with contemporary adaptations in leaf gas exchange enabling accelerated stem growth under cleaner air conditions. These differential species responses underscore shifts in species competition, whereby European beech is gaining dominance as Norway spruce recedes. Our study integrates tree-growth dynamics with physiological and nutrient availability trends, revealing the pivotal role of atmospheric chemistry changes in shaping temperate forest ecosystems and enhancing interspecies competition dynamics.