Tree stem diameter variations and transpiration in Scots pine: an analysis using a dynamic sap flow model.

A dynamic model for simulating water flow in a Scots pine (Pinus sylvestris L.) tree was developed. The model is based on the cohesion theory and the assumption that fluctuating water tension driven by transpiration, together with the elasticity of wood tissue, causes variations in the diameter of a tree stem and branches. The change in xylem diameter can be linked to water tension in accordance with Hookeâ s law. The model was tested against field measurements of the diurnal xylem diameter change at different heights in a 37-year-old Scots pine at Hyytiälä, southern Finland (61 degrees 51' N, 24 degrees 17' E, 181 m a.s.l.). Shoot transpiration and soil water potential were input data for the model. The biomechanical and hydraulic properties of wood and fine root hydraulic conductance were estimated from simulated and measured stem diameter changes during the course of 1 day. The estimated parameters attained values similar to literature values. The ratios of estimated parameters to literature values ranged from 0.5 to 0.9. The model predictions (stem diameters at several heights) were in close agreement with the measurements for a period of 6 days. The time lag between changes in transpiration rate and in sap flow rate at the base of the tree was about half an hour. The analysis showed that 40% of the resistance between the soil and the top of the tree was located in the rhizosphere. Modeling the water tension gradient and consequent woody diameter changes offer a convenient means of studying the link between wood hydraulic conductivity and control of transpiration.

[1]  Pertti Hari,et al.  Trees as a water transport system. , 1986 .

[2]  P. G. Jarvis,et al.  STOMATAL CONDUCTANCE AND PHOTOSYNTHESIS IN A MATURE SCOTS PINE FOREST I. DIURNAL, SEASONAL AND SPATIAL VARIATION IN SHOOTS , 1985 .

[3]  John Finn Siau,et al.  Transport Processes in Wood , 1984, Springer Series in Wood Science.

[4]  J. Grace,et al.  Continuous measurements of water tensions in the xylem of trees based on the elastic properties of wood , 1997, Planta.

[5]  M. Zimmermann.  Xylem Structure and the Ascent of Sap , 1983, Springer Series in Wood Science.

[6]  E. Schulze,et al.  Hydraulic and osmotic properties of spruce roots , 1994 .

[7]  Melvin T. Tyree,et al.  A new stem hygrometer, corrected for temperature gradients and calibrated against the pressure bomb , 1984 .

[8]  P. Hari,et al.  Long-term field measurements of atmosphere-surface interactions in boreal forest combining forest ecology, micrometeorology, aerosol physics and atmospheric chemistry , 1998 .

[9]  P. Jarvis,et al.  A dynamic model for studying flow of water in single trees. , 1986, Tree physiology.

[10]  Reversing cavitation in tracheids of Pinus sylvestris L. under negative water potentials , 1994 .

[11]  N. Holbrook.  Stem Water Storage , 1995 .

[12]  C. Westman.  A simple device for sampling of volumetric forest soil cores , 1995 .

[13]  H. Helmisaari,et al.  Seasonal and yearly variations of fine-root biomass and necromass in a Scots pine (Pinus sylvestris L.) stand , 1998 .

[14]  T. Aalto.  Carbon Dioxide Exchange of Scots Pine Shoots as Estimated by a Biochemical Model and Cuvette Field Measurements , 1998 .

[15]  A. Brown,et al.  Pinus Sylvestris L. , 1968 .

[16]  F. Berninger,et al.  Correlations of Pipe Model Parameters with Climatic Variables and Stand Characteristics , 1997 .

[17]  A. Haase,et al.  Xylem water transport: is the available evidence consistent with the cohesion theory? , 1994 .

[18]  C. Field,et al.  Negative Xylem Pressures in Plants: A Test of the Balancing Pressure Technique , 1995, Science.

[19]  Hartmut Bossel,et al.  Modelling forest dynamics: Moving from description to explanation , 1991 .

[20]  William T. Pockman,et al.  Sustained and significant negative water pressure in xylem , 1995, Nature.

[21]  S. Running.  Field Estimates of Root and Xylem Resistances in Pinus contorta using Root Excision , 1980 .

[22]  P. Hari,et al.  An improvement of the method for calibrating measurements of photosynthetic CO2 flux , 1999 .

[23]  J. Grace.  Water Transport in Plants under Climatic Stress: Refilling of embolized xylem , 1993 .

[24]  P. Hari,et al.  Effect of variations of PAR on CO2 exchange estimation for Scots pine , 2000 .

[25]  Lars Tirén.  Om barrytans storlek hos tallbestånd , 1927 .

[26]  M. Tyree,et al.  A dynamic model for water flow in a single tree: evidence that models must account for hydraulic architecture. , 1988, Tree physiology.

[27]  M. G. Ryan,et al.  Evidence that hydraulic conductance limits photosynthesis in old Pinus ponderosa trees. , 1999, Tree physiology.

[28]  F. Berninger,et al.  Foliage area-sapwood area relationships of Scots pine (Pinus sylvestris) trees in different climates , 1994 .

[29]  A. Mäkelä,et al.  Field evidence for the optimality hypothesis of gas exchange in plants , 1999 .

[30]  G. Campbell.  Fundamentals of Radiation and Temperature Relations , 1981 .

[31]  L. Salmén.  Thermal Expansion of Water-saturated Wood , 1990 .

[32]  P. F. Scholander,et al.  Sap Pressure in Vascular Plants , 1965, Science.

[33]  Abhijit Nagchaudhuri,et al.  Time constant for water transport in loblolly pine trees estimated from time series of evaporative demand and stem sapflow , 1997, Trees.

[34]  L. Marklund,et al.  Biomass functions for pine, spruce and birch in Sweden , 1988 .