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Extreme droughts induced by climate change have led to drought-induced die-off events in several parts of the world. Such events have been observed for pine and other species, in particular regions across Europe and southwest of North American. Previous studies have demonstrated the relationship betweenspecies diversityandresistance to droughtin forest ecosystems under certain environmental conditions. However, despite the potential benefits of multi-species interactionson forest resistance to drought, little is known in terms of its underlying mechanisms which drivethe positive and/or negative feedbacks at both above-andbelow-ground levels.To understand the underlying mechanisms and their relationships with biotic and abiotic covariates, I propose a project to exam the effect of species-interactions on drought response in both a mesocosmsunder controlledgrowth environment and in a field experimentsettings. The main objects of the project are to characterize (1) above-ground physiological responses on stomatal vs. non-stomatal drought response, (2) below-ground soil water uptake dynamics, (3) whole plant carbon allocation patterns, and (4) carbon isotope composition and water use efficiencyof tree seedlingsgrowing under different species interactionsand soil water conditions. I plan to employ both leaf gas exchange techniques and isotope labelling methods to quantify the above objects. Two of the most common species in Europe, Scots pine and Sessile oak, will be used as the model species.