No variation in embolism resistance driven by aridity in a widely distributed clone of Fagus sylvatica

Water moves through trees pulled under tension through a series of dead tubes called xylem. During drought, conduits can be invaded by air, causing an embolism, leading to tissue or whole-plant death. Fagus sylvatica is the most abundant European broadleaf forest tree, and is currently under threat due to an increasing frequency and severity of drought, resulting in xylem embolism, dieback, and death. Here, we investigated the variation in embolism resistance across globally distributed individuals of F. sylvatica f. purpurea receiving between 563 mm and 1362 mm of rainfall per year, as well as variation in embolism resistance across the canopy. We found no difference in the water potential when 50% of the stem xylem was embolized (P₅₀) across locations in this clonal form of F. sylvatica but we did find variation in P₅₀ across the canopy driven by light, with shade branches being significantly more vulnerable than part or full sun-adapted branches. The lack of variation in response to annual rainfall in a globally distributed clone has implications for predicting the risk of mortality driven by periodic droughts and long-term shifts in rainfall patterns due to climate change in F. sylvatica. Our work also highlights the importance of horticultural resources such as globally distributed clones as a model system for examining plant responses to the environment.