Exploring root water uptake of beech and spruce trees across Europe

Ecohydrological studies aiming to understand patterns in root water uptake by trees based on plant and soil water isotope data are often confined to one or a few nearby locations. In this study, we took advantage of a recently established pan-European hydrogen (δ²H) and oxygen (δ¹⁸O) isotope dataset (10.16904/envidat.542) to assess root water uptake depth for beech and spruce trees across Europe. For a subset of sites, δ¹⁷O data were available as well.

Our analysis revealed consistent isotopic enrichment in xylem water of spruce trees compared to beech trees across all mixed-species sites (N=13), suggesting that spruce predominantly used shallower soil water regardless of environmental conditions. Additionally, we observed isotopic enrichment in stem xylem water from spring to summer at most beech and spruce sites (N=32), suggesting both species relied on isotopically enriched summer precipitation. Interestingly, for a subset of sites (N=8), there was an inverse pattern, with isotopic depletion in summer, implying shifts to deeper soil water sources or uptake of shallow soil water that was isotopically depleted in summer compared to spring conditions.

To further explore these findings, we will visually and statistically examine them using isotope data from the soil (10–90 cm depth). We will analyze the role of climate (using gridded data), alongside site-, soil-, and tree-specific metadata to better understand the factors influencing the variation in root water uptake at the continental scale. Additionally, we will explore the potential of oxygen-17 excess to provide further insights into root water uptake dynamics.

Lehmann et al., 2025. Soil and stem xylem water isotope data from two pan-European sampling campaigns. Earth System Science Data, 17, 6129–6147, https://doi.org/10.5194/essd-17-6129-2025