Darius Valūnas, Jonas Mažeika, Rūtilė Pukienė, Miglė Stančikaitė, Žana Skuratovič, Adomas Vitas, Rita Karabanovienė, Sandra Metslaid

Climatic dominance and delayed industrial modulation of inter-site intrinsic water-use efficiency in Scots pine revealed by tree-ring δ¹³C

Abstract Tree-ring stable carbon isotopes provide insights into long-term physiological responses of forests to environmental change. This study examined inter-site divergence in intrinsic water-use efficiency (ΔiWUE) and radial growth (ΔBAI) of Scots pine (Pinus sylvestris L.) at two sites in northern Lithuania from 1933 to 2022. One site is located near a major historical source of industrial emissions, while the other represents a comparatively less affected environment. Tree-ring δ¹³C data were used to reconstruct iWUE, and inter-site differences were analysed in relation to climatic variability and reconstructed emission histories. Both physiological and growth chronologies showed increasing divergence beginning in the early 1990s. Mean ΔiWUE increased significantly after 1990, while ΔBAI shifted from negative to positive values, indicating a reversal in relative growth performance. Inter-site differences in iWUE were moderately correlated with growth divergence (r = 0.45, p < 0.001). Generalized additive models identified climatic variability as the dominant driver of iWUE divergence. Differences in growing-season precipitation showed a significant nonlinear relationship with ΔiWUE and explained the largest proportion of deviance among climatic predictors. After accounting for temporal trends and climatic divergence, models including industrial emissions revealed additional nonlinear effects. One-year lagged sulfur dioxide showed the strongest relationship with ΔiWUE, while lagged carbon monoxide improved model performance; nitrogen oxides had no significant effect. These results indicate that climatic variability, particularly moisture availability, primarily controls inter-site physiological divergence, while industrial emissions exert secondary, lagged influences.

Doi https://doi.org/10.5200/baltica.2026.2.3

Keywords Tree-ring stable isotopes; iWUE; whole-wood; air pollution; climatic variability; stomatal conductance; generalised additive model (GAM); Eastern Baltic

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