Sap-flow velocity reduction by soil water deficit observed in a Lithocarpus edulis forest on Kyushu Island, Japan

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  • Komatsu Hikaru
    Division of Forest Ecosphere and Management, Department of Forestry and Forest Products Science, Faculty of Agriculture, Kyushu University
  • Katayama Ayumi
    Division of Forest Ecosphere and Management, Department of Forestry and Forest Products Science, Faculty of Agriculture, Kyushu University
  • Kume Tomonori
    Division of Forest Ecosphere and Management, Department of Forestry and Forest Products Science, Faculty of Agriculture, Kyushu University
  • Otsuki Kyoichi
    Division of Forest Ecosphere and Management, Department of Forestry and Forest Products Science, Faculty of Agriculture, Kyushu University

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Other Title
  • 九州のマテバシイ林で計測された土壌水分減少による樹液流速の低下

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Abstract

This paper examines transpiration reduction due to soil water deficits observed in a Lithocarpus edulis forest on Kyushu Island, south-western Japan. Continuous sap flow measurements were performed on six trees to monitor changes in tree transpiration rates. A reduction in sap flow velocity was observed in the period between late-September and late-October 2003. Precipitation amounts for this period were limited resulting in a corresponding low soil matric potential. A clear reduction in sap flow velocity occurred when soil matric potential at a 10 cm depth was ＜ － 70 ( kPa) . Sap flow velocity scaled for 1. 0 kPa vapor pressure deficit declined by 42 ％ when soil matric potential at a 10 cm depth was ＜ － 70 (kPa) compared to ≥ － 70 ( kPa) . In addition, intensive leaf-scale physiological measurements were performed on two days that had contrasting soil matric potentials. The intensive measurements showed lower leaf transpiration rates and stomatal conductance on the day with the lower soil matric potential. This finding suggests soil water deficits caused stomatal closure and therefore reduction in tree transpiration. Sap flow velocity and leaf water potential data showed that stem hydraulic conductance did not decline with low soil matric potential when compared to the day with higher soil matric potential.

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