AbstractKey messageIn a mixed,Fagus sylvaticaL.-Acer pseudoplatanusL., young plantation, trees of both species absorbed water from superficial soil layers despite the presence of roots and water in deeper layers. Admixture proportion and tree density were weak predictors of water acquisition depth, as well as fine root vertical distribution, although it might be due to distinct periods of root and isotope investigations.ContextPromoting mixed forests and reducing stand densities have been proposed as effective ways to maintain the productivity of temperate planted forest stands in a changing climate.AimsThe objective of this study was to analyse how stand density and the degree of admixture of European beech and sycamore maple interactively influenced the water acquisition profile of individual trees.MethodsWe used a stable isotope (deuterium) approach to determine the profiles of soil water acquisition of both species in a 16-year-old plantation where trees had been planted along crossed gradients of tree density and species proportion. The profiles were then compared with the vertical distribution of fine root of these species in the plantation.ResultsAll the target trees mostly absorbed soil water from the first few centimetres of soil despite homogenous vertical water availability and the fact that a great part of the fine root biomass was located below 10 cm. Admixture proportion and tree density had negligible effects on soil water acquisition depth.ConclusionNo vertical differentiation of soil water acquisition between the two species was observed, suggesting that mixing these species does not promote reduction of belowground competition for resource acquisition. The vertical distribution of fine root may be a weak predictor of water acquisition depth.