Simulated and measured water uptake by picea abies under non-limiting soil water conditions

Abstract

A one-dimensional non-steady-state soil-plant-atmosphere continuum (SPAC) model was applied to a stand of Picea abies trees in southern Sweden. The simulated root water uptake was compared with measured sap flow under non-limiting soil water conditions. Sap flow was measured during the growing season using the tree-trunk heat balance method. The model included four resistances against water (soil-root, plant, stomatal and aerodynamic), one pool of easily available plant water and one compartment of intercepted water on the needle surface. The bulk stomatal resistance was estimated as the product of the combined effect of two independent variables—vapour pressure deficit and solar radiation. Good agreement between simulated and ‘measured’ water uptake was obtained both on short- and long-term scales, and the model explained 92–93% of the variation of measured uptake for both hourly and daily values. The pool of easily available water was found to be small (0.5 mm), i.e. of the same order as for agricultural crops.