Báo cáo lâm nghiệp: " Diurnal evolution of water flow and potential in an individual spruce: experimental and theoretical study"

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Diurnal evolution of water flow and potential in an individual spruce: experimental and theoretical study P. Cruiziat A. Granier J.P. Claustres 1 2 1 1 D. Lachaize 1 Laboratoire de Bioclimatologie, INRA, Domaine-de-Crouelle, F-63039 Clermont-Ferrand, and 2 Nancy, INRA, Station de Sylviculture, BP 35, F-54280 Seichamps, France CRF de Introduction Assumptions 1. Sap moves from points of high potential to points of low potential. 2. Flow within the We present a model built primarily to study different parts of the system obeys the Darcy equation. 3. Roots are not supposed to have the water flow in a single tree within a a capacitance (optional). 4. All parameters forest. After comparing it with other avail- 5. Neither branch, are lumped together. able systems, we develop the characteris- twig architecture nor growth are considered tics of our model and its usefulness. (optional). Values of the parameters and input variables The data consist of hourly measurements of Materials and Methods sap flow (bottom of the trunk), leaf water poten- tial at 2 levels and transpiration rate per tree (calculated by the Penman-Monteith equation for the stand). In addition, sapwood cross sec- Outline of the model tional.area and dimensional characteristics at The structure of the model (Fig. 1) comes from different levels provide information for starting idea of how the spruce we work with is our values of the parameters (resistances and compartmented; 7 compartments were distin- capacitances). Then they were adjusted (by trial guished: leaves (1uppercrown (2), lower and error) in order to obtain a combination of crown (2), trunk (2). Except for leaves, 2 kinds values which reasonably fit our measurements. of water reservoirs constitute each of the 3 pre- ceding levels (Jarvis, 1975; Granier, 1987; Gra- nier and Claustres, 1989): a small one corre- Properties sponding to the elastic tissues with a small constant of time and a larger one representing Under ’ideal’ conditions (regular transpiration, the sapwood with a large time constant. Twelve all potentials, including V1 starting at 0 MPa), soil resistances must be specified. Although SPICE, there is a continuous evolution of in the W the circuit simulation program we used, allows different parts of the tree (Fig. 2); only the us to introduce variable capacitances and resis- reservoirs from elastic tissues show no residual tances (Cruiziat and Thomas, 1988), we did not deficit at the end of the night; the sapwood think they were necessary at this stage of our tissue still stays at a negative yq its contribution experimental knowledge. is about 3% of the daily transpiration. This
balance of drainage basins to this increases gradually if the yr!!;, falls simplified proportion use version as a subrnodel. for several days. The difference between maximum rates of transpiration (E and absorption is greatly ) max affected by the relative magnitude of root resis- tance. Discussion and Conclusions The minimum value of leaves occurs leaves about 1 h after (E at that time, transpiration ): max and absorption are equal. This fact provides a means to obtain an estimation of the total re- This model was designed to be a working sistance of the transpirational pathway (Fig. 3). tool. It has 2 main purposes: 1) to contin- It is possible to determine the 3 parameters experimental uously bring together new (2 resistances and 1 capacitance) of the equi- coherent representation; and data within a valent circuit having the same transfer function to help us to select the most crucial 2) (= transpiration versus absorption). This trans- measurements. Our model differs from formation allows those interested in water
other for different published models (Landsberg et al., different models designed 1976; Milne and Young, 1985; Wronski et objects. al., 1985; Edward et al., 1986) by its struc- ture. Nevertheless, for the moment, due to the lack of experimental data, it is likely References that several models of the same object (e.g., same species) can be presented, Cruiziat P. & Thomas R. (1988) SPICE, a circuit each having its own strengths and simulation program for physiologists. Agrono- weaknesses. Therefore, we believe that it mie 8, 49-60 is more useful to compare different ap- Edwards W.R.N., Jarvis P.G., Landsberg J.J. & Talbot H. (1986) A dynamic model for studying proaches to the same object rather than
Vries D.A. & Afgan N.H., eds.), John Wiley & flow of water in trees. Tree Physiol. 1, single Sons, New York, pp. 369-394 309-324 Landsber J.J., B!lanchard TW. & Warrit B. (1976) g Granier A. (1987) Mesure du flux de s6ve Studies on the movement of water through apple brute dans le tronc du Douglas par une trees. J. Exp. Bot. 27, 579-596 nouvelle m6thode thermique. Ann. Sci. For. 44, 1-14 4 Milne R. & Yourng P. (1985) Modelling of water movement in trees. In: IFAC Identification and Granier A. & Claustres J.P. (1989) Relations System Parameter Estimation, York, U.K., pp. hydriques dans un 6pic6a (Picea abies L.) en 463-468 conditions naturelles: variations spatiales. Oecol. Plant. 2, in press Wronsky E.B., Holmes J.W. & Turner N.C. (1985) Phase and amplitude relations between Jarvis P. (1975) Water transfer in plants. In: transpiration, water potential and stem shrink- Heat and Mass Transfer in the Biosphere. Part 1. Transfer Processes in Plant Environment. (de age. Plant Cell E’nviron. 8, 613-622