Poster: Water Relations
Abs #
208: Modelling the diurnal rhythm of water flow in young oak and beech trees
The water flow through individual trees is a very dynamic process. The water loss through the leaves initiates the water movement within the tree and, depending on the time of the day, water is withdrawn from either the internal water reserves of the tree and/or directly from the soil. The dynamic water flow through young model trees of oak (Quercus robur L.) and beech (Fagus sylvatica L.) was investigated using a specially equipped growth chamber for studies of plant-water relationships. A complex set of physiological processes (transpiration rate, sap flow rate at root, stem and branch level, together with diameter fluctuations) were continuously measured at 10 min intervals. The microclimatological variables driving these processes were recorded as well. This special arrangement of instruments aimed at determining the diurnal dynamics of water flow and water storage in the model trees, and to provide a dataset which can be used for model validation. The dynamic flow and storage of water could be modelled using two different approaches, i.e. (1) as an electrical RC circuit and (2) as a hydraulic flow system. The models contain different system components based on both physical and physiological characteristics which differ between oak (ring-porous tree) and beech (diffuse-porous tree). Both models use transpiration rate as an input variable and they simulated the diurnal courses of stem sap flow, water storage and stem diameter fluctuation successfully. The model parameters are related to dynamic water transport characteristics such as response time, hydraulic capacitances and hydraulic resistances. The differences observed between the oak and the beech trees could be explained by 3D images of xylem morphology obtained from micro-tomographic analysis.
