STEMCELL · Unified theory for water availability impacts on mature tree water use and wood cell formation in forest stems

Trees play a key role in regulating the global terrestrial water and carbon cycles by controlling water loss through leaves and directing carbon into stems to form wood. In doing so, forests capture substantial amounts of anthropogenic carbon, a crucial process shaping international climate mitigation policies. However, increasing atmospheric and soil water deficits have raised global concerns about the resilience of wood formation in European forests. Predicting how environmental changes will affect wood formation and related ecosystem services remains difficult due to unclear underlying mechanisms. Recent studies identify turgor as a critical link between tree water-use strategies and wood growth, providing new insights into tree responses to water stress. Before application, this concept must be tested, validated, and integrated into forest growth and carbon models.STEMCELL aims to uncover the relationship between whole-tree water use and wood cell formation in mature trees, using turgor-driven growth models to predict the future of wood formation and carbon allocation in forests facing drier conditions. STEMCELL will integrate experimental, observational, and modelling approaches. Controlled experiments on juvenile trees will be scaled up to mature trees at unique whole-ecosystem rainfall exclusion experiments, carefully monitoring wood formation. These experiments will drive the development of a new numeric model simulating wood formation responses to drought, validated using one of Europe’s largest databases of tree growth, wood structure, and water use.Through the outlined work, STEMCELL will build a solid physiological and mechanistic foundation for predicting the effects of climate change on wood formation and the global carbon cycle. Given the ecological and economic importance of forest ecosystems, the project's outcomes will be critical for guiding science-based forest management and conservation efforts aimed at strengthening ecosystem resilience.