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Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp Original article đề tài: Variability of stomatal conductance in the crown of a maritime pine (Pinus pinaster Ait.). | 426s Ann. Sci. For. 1989 46 suppl. 426s-428s Forest Tree Physiology E. Dreyer et al. eds. Elsevier INRA Variability of stomatai conductance in the crown of a maritime pine Pinus pinaster Ait. D. Loustau and F. El Hadj Moussa with the technical assistance of M. Sartore and M. Guedon Laboratoire de Sylviculture et d Ecologie INRA Station de Recherches Forestieres de Pierroton Domaine-de-l Hermitage 33610 Cestas France Introduction Stomatai response of conifers to environmental variables such as air water vapor deficit has been reported by many authors Whitehead et al. 1984 Sandford and Jarvis 1986 . Variations of stomatai conductance gs related to needle age and situation in the canopy have also been described Leverenz et al. 1982 Tan eta . 1977 . In order to estimate a general pattern of stomatai conductance gs in the crown of a maritime pine the effects of each of these sources of variability have been assessed. For each of the 30 shoots measurements were made on a pair of needles of a single fascicle of the shoot. Measurements of the whole sample were made on 5 d from 07 00 to 19 00 U.T. between June 2 and August 30 1988. An automatic steady state porometer LICOR 1600 was used with a chamber of 63 cc internal volume. gs was expressed in cm s on a total leaf area basis. During the experiment hourly means of temperature relative humidity wind speed and irradiance were calculated from micrometeorologi-cal measurements made 2 m above the canopy Hourly means of canopy transpiration were also computed from sap flow measurements Granier 1985 on a sample of 10 pines including the sample tree . Results Materials and Methods All measurements were made in the crown of a single standard tree from an 18 yr old stand of maritime pine mean height 12 m mean circumference at B.H. 61 cm . A sample of shoots was stratified with respect to whorl height 8 levels branch orientation 9 levels and needle age 3 levels . Seasonal pattern In the course of the experiment a dry period began on
