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P4 - Tree Physiology (water relations)

Water relations of beech and interacting vegetation in beech-dominated forests. Institute of Forest Botany and Tree Physiology, University of Freiburg.

Three highly interconnected though independet approaches [a) xylem flow measurements, b) stable isotope analysis/modelling, c) a hydrodynamic model system PLATHO/Expert-N] are applied for assessing water relations of trees and co-occurring vegetation on different time-scales on a whole plant level. Water flow / movement within the plant and partitioning between species will be modelled and additionally analysed using sap flow sensors, leaf level gas exchange and by tracing δ18O and δD in potential water sources and in xylem water. Δ18O, ΔD and δ13C in organic pools with different turn-over times will be assessed to characterise responses of stomatal conductance (gs) and transpiration (T) to environmental conditions. In addition, isotopic signatures will be used to predict gs and T applying process-oriented models. Based on the model system Expert-N and the functional-structural plant growth model PLATHO a tree hydrodynamic model for beech will be developed. The model will be applied to simulate soil-plant-air system water relations including mycorrhiza effects on water uptake from soil and will be inserted as tree water flow sub-model to the ecosystem-scale model. Both, the isotopic approach and the hydrodynamic model will be calibrated and validated with measurements at the three field sites. Cross-validation between the two independent approaches will be carried out at additional field sites.

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