Water flow and hydraulic characteristics of Japanese red pine and oak trees
To assess the characteristics of water flow in a tree and the contribution\nof the stem water storage to transpiration, some field observations\nwere carried out in two natural forests: a Japanese red pine (Pinus\ndensiflora Sieb. et Zucc.) forest and an oak (Quercus mongolica Fish)\nforest. Water potentials of leaf, stem, root and soil water, sap\nflow rate, volumetric water content of the stem and micrometeorological\nfactors were measured during the observation periods. Clear diurnal\nvariations in volumetric water content of a stem were observed. It\nwas confirmed that water storage in the stem contributed to the transpiration\nprocess. This contribution appeared when the difference in water\npotential between the root and stem was more than 0·3 MPa. The stem\nwater storage was extracted by the driving force due to the difference\nof the response of the root and stem water potential to change in\nthe leaf water potential in daytime. The stem capacitance of 1·44\nkg MPa-1 for the Japanese red pine and 0·44 kg MPa-1 for the oak\nwere evaluated from the variation in the water storage in the stem\nand the difference of water potential between root and stem. Evaluations\nof the water budget were made for each test stand. The results indicated\nthat the contribution of water storage in the stem to transpiration\naccounted for 10 to 20% of the daily transpiration. Copyright © 2001\nJohn Wiley & Sons, Ltd.