Leaf water isotopic enrichment (ΔD[LW]) is the original source of climatic information stored in tree-ring δ¹⁸O and δD. Tree-ring δ¹⁸O temporal variability has been correlated to environmental variables such as temperature, precipitation, relative humidity (RH), and phenomena such as tropical cyclones and drought. Meanwhile, more development is needed to use tree-ring δD temporal variability as a paleoclimatic bioindicator. An increased understanding of the climatic signal of ΔD[LW] could help to better interpret temporal variability of tree-ring δD. Leaf-water δ¹⁸O enrichment (Δ¹⁸O[LW]) exhibits stronger relationships to environmental variables such as RH, and physiological rates such as transpiration rate, compared to ΔD[LW]. ΔD[LW] has been correlated to the disequilibrium between atmospheric water vapor δD (δD[WV]) and plant-stem water δD. New evidence shows that δD[WV] in forests varies diurnally, and such variability is related to ecosystem-level processes such as evapotranspiration. Such relationships suggest that ecosystem-level processes in forests can participate a role in the disequilibrium between δD[WV] and plant-stem water δD. Resultantly, there is a potential for ΔD[LW] to exhibit previously unidentified correlations to ecosystem-level processes. In this study, we aimed to explore the potential of ΔD[LW] as a bioindicator of ecosystem-level processes such as evapotranspiration and gross primary productivity. We used a temporal survey of P. sylvestris ΔD[LW], Δ¹⁸O[LW] and eddy covariance data during 2019 at Hyytiälä, central Finland. This poster shows comparisons of ΔD[LW] and Δ¹⁸O[LW] to climatic variables and ecosystem processes for new insights about ΔD[LW] as a bioindicator of ecosystem-level processes.