© 2005 Heron Publishing—Victoria, Canada
Influences of environmental factors on the radial profile of sap flux density in Fagus crenata growing at different elevations in the Naeba Mountains, Japan
Mitsumasa Kubota (1, 2), John Tenhunen (3), Reiner Zimmermann (4), Markus Schmidt (3), Samuel Adiku (3) and Yoshitaka Kakubari (1)
1. Institute of Silviculture of Forest Resources, Faculty of Agriculture, University of Shizuoka, Ohya 836, Shizuoka 422-8529,
Japan / 2. Corresponding author (kubota@earth.ocn.ne.jp) / 3. Department of Plant Ecology, University of Bayreuth, 95440 Bayreuth, Germany / 4. Max Planck Institute for Biogeochemistry, P.O. Box 100164, D-07743 Jena, Germany / Received June 15, 2004; accepted October 15, 2004; published online March 1, 2005
Summary
Sap flux density was measured continuously during the 1999 and 2000 growing seasons by the heat dissipation method in natural
Fagus crenata Blume (Japanese beech) forests growing between 550 and 1600 m on the northern slope of the Kagura Peak of the Naeba Mountains,
Japan. Sap flux density decreased radially toward the inner xylem and the decrease was best expressed in relation to the number
of annual rings from the cambium, or in relation to the relative depth between the cambium and the trunk center, rather than
as a function of absolute depth. The relative influences of radiation, vapor pressure deficit and soil water on sap flux density
during the growing season were similar for the outer and inner xylem, and at all sites. Measurements of soil water content
and water potential at a depth of 0.25 m demonstrated that sap flux density responded similarly and sensitively to water potential
changes in this soil layer, despite large differences in rooting depth at different elevations, localizing one important control
point in the functioning of this forest ecosystem. Identification of the relative influences of radiation, vapor pressure
deficit and drying of the upper soil layer on sap flux density provides a framework for in-depth analysis of the control of
transpiration in Japanese beech forests. In addition, the finding that the same general controls are operating on sap flux
density despite climate gradients and large differences in overall forest stand structure will enhance understanding of water
use by forests along elevation gradients.
Keywords:
annual rings, diffuse-porous, drought, Granier sensor, photosynthetic photon flux, radial pattern, soil water, vapor pressure
deficit.
