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

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Báo cáo lâm nghiệp: " Diurnal evolution of water flow and potential in an individual spruce: experimental and theoretical study"Diurnal evolution of water flow and potential inan individual spruce: experimental and theoretical studyP. Cruiziat A. Granier J.P. Claustres 1 2 1 1 D. Lachaize1 Laboratoire de Bioclimatologie, INRA, Domaine-de-Crouelle, F-63039 Clermont-Ferrand, and2 Nancy, INRA, Station de Sylviculture, BP 35, F-54280 Seichamps, France CRF deIntroduction Assumptions 1. Sap moves from points of high potential to points of low potential. 2. Flow within theWe present a model built primarily to study different parts of the system obeys the Darcy equation. 3. Roots are not supposed to havethe water flow in a single tree within a a capacitance (optional). 4. All parametersforest. After comparing it with other avail- 5. Neither branch, are lumped together.able systems, we develop the characteris- twig architecture nor growth are consideredtics of our model and its usefulness. (optional). Values of the parameters and input variables The data consist of hourly measurements ofMaterials 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 atThe structure of the model (Fig. 1) comes from different levels provide information for starting idea of how the spruce we work with isour values of the parameters (resistances andcompartmented; 7 compartments were distin- capacitances). Then they were adjusted (by trialguished: leaves (1uppercrown (2), lower and error) in order to obtain a combination ofcrown (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- Propertiessponding to the elastic tissues with a smallconstant 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), soilresistances must be specified. Although SPICE, there is a continuous evolution of in the Wthe circuit simulation program we used, allows different parts of the tree (Fig. 2); only theus to introduce variable capacitances and resis- reservoirs from elastic tissues show no residualtances (Cruiziat and Thomas, 1988), we did not deficit at the end of the night; the sapwoodthink they were necessary at this stage of our tissue still stays at a negative yq its contributionexperimental knowledge. is about 3% of the daily transpiration. This balance of drainage basins to this increases gradually if the yr!!;, falls simplifiedproportion use version as a subrnodel.for several days. The difference between maximum rates oftranspiration (E and absorption is greatly ) maxaffected by the relative magnitude of root resis-tance. Discussion and Conclusions The minimum value of leaves occurs leavesabout 1 h after (E at that time, transpiration ): ...