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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: Water movement and its resistance in young trees of Cryptomeria japonica. | 361s Ann. Sci. For. 1989 46 suppl. 361s-365s Forest Tree Physiology E. Dreyer et al. eds. Elsevier INRA Water movement and its resistance in young trees of Cryptomeria japonica H. Yahata Laboratory of Silviculture Department of Forestry Faculty of Agriculture Kyushu University Fukuoka Japan Introduction Information about water flow resistance is essential to understanding and simulating water movement in trees Yahata 1987 . There are a number of papers concerned with it for some species but few for Cryptomeria japonica and no data are available on the gradient of water potential in intact stem. This study was undertaken to examine whether the resistance in stems would be regarded as substantially constant all day long and to find a simple equation to predict the effect of stem form on it. Materials and Methods 14 yr old c. japonica trees growing in a plantation of high stand density about 6650 stems per ha were used. Psychrometer sensors Wescor PCT55-30 were used with an automated recording system for measuring the water potential of soil at a depth of 20 cm and rootstock at 10 cm and a Scholander pressure chamber for shoots. The sensors were placed and sealed in small drilled holes in the stem and rootstock. Diurnal variation of the ambient temperature of the sensors was minimized to within less than 1 c by the use of insulating materials to reduce errors from temperature gradients. Transpiration rates were estimated by the measurement of leaf conductance to water vapor and the ambient vapor deficit between leaf and air. The water flow rates in the stem at different heights 0.5-2.5 m were estimated using the relationships between the heat-pulse velocity measured with an automatic multichannel recording system Yahata 1984 and the water uptake rates from the severed basal stem at the end of a series of measurements of the intact tree. Sapwood conducting area was measured by using a dye 1 solution of acid fuchsine . Water flow rate Q is customarily expressed as an .
