© 2007 Heron Publishing—Victoria, Canada
Effects of ring-porous and diffuse-porous stem wood anatomy on the hydraulic parameters used in a water flow and storage model
Kathy Steppe (1, 2) and Raoul Lemeur (1)
1. Faculty of Bioscience Engineering, Department of Applied Ecology and Environmental Biology, Laboratory of Plant Ecology, Ghent
University, Coupure links 653, B-9000 Ghent, Belgium / 2. Corresponding author (kathy.steppe@UGent.be) / Received November 23, 2005; accepted February 15, 2006; published online October 2, 2006
Summary
Calibration of a recently developed water flow and storage model based on experimental data for a young diffuse-porous beech
tree (Fagus sylvatica L.) and a young ring-porous oak tree (Quercus robur L.) revealed that differences in stem wood anatomy between species strongly affect the calibrated values of the hydraulic
model parameters. The hydraulic capacitance (C) of the stem storage tissue was higher in oak than in beech (939.8 versus 212.3 mg MPa–1). Model simulation of the elastic modulus (ε) revealed that this difference was linked to the higher elasticity of the stem
storage tissue of oak compared with beech. Furthermore, the hydraulic resistance (Rx) of beech was about twice that of oak (0.1829 versus 0.1072 MPa s mg–1). To determine the physiological meaning of the Rx parameter identified by model calibration, we analyzed the stem wood anatomy of the beech and oak trees. Calculation of stem
specific hydraulic conductivity (ks) of beech and oak with the Hagen-Poiseuille equation confirmed the differences in Rx predicted by the model. The contributions of different vessel diameter classes to the total hydraulic conductivity of the
xylem were calculated. As expected, the few big vessels contributed much more to total conductivity than the many small vessels.
Compared with beech, the larger vessels of oak resulted in a higher ks (10.66 versus 4.90 kg m–1 s–1 MPa–1). The calculated ratio of ks of oak to beech was 2, confirming the Rx ratio obtained by model calibration. Thus, validation of the Rx parameter of the model led to identification of its physiological meaning.
Keywords:
elasticity, Fagus sylvatica, Hagen-Poiseuille equation, hydraulic capacitance, hydraulic conductivity, hydraulic resistance, microCT, Quercus robur, sap flow, stem specific hydraulic conductivity, X-ray computed microtomography.
