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Hydraulic resistance of main stems and petiols of Pasania edulis Makino was measured by pressure chamber to clarify the distribution of hydraulic resistance in sun shoots at the top of crown (sunny co...nditions) and shade shoots at the bottom of crown (shaded conditions). Hydraulic conductance was higher in sun shoots than in shade shoots. A clear relationship was obtained between the hydraulic conductance of the main stem and cumulative leaf area. This relationship confirmed the pipe model theory from the view point of water conduction. Leaf specific resistance per unit stem length, derived from the relationship between leaf specific resistance and conductive distance of the main stem, was constant in several sun shoots. Conversely, the effect of conductive distance on leaf specific resistance in shade shoots can be ignored. Leaf specific resistance of petiols was greater than that of main stems in all shoots. In particular, the percentage of leaf specific resistance of petiols in the total shoot resistance was about 90% in sun shoots. This result suggests that petiolar resistance is a limiting factor, analogous to a bottle neck in the movement of water in shoots. The strong regulation of water movement at petiols in the sun shoots was thought to help avoid catastrophic water loss of total shoots under high transpirational demand.
マテバシイの陽樹冠および陰樹冠内の水分通導抵抗の分布を明らかにする目的で，当年生シュートの主軸および薬柄部の水分通導抵抗をプレッシャー・チャンバーを用いて測定した．主軸の水分通導性は陽樹冠で陰樹冠よりも高く，通導距離よりも通導面が支持する葉面積との間で明瞭な関係が認められた．これによって樹形のパイプモデルを水分通導機能面から検証できた．さらに，葉面積ベースでの水分通導抵抗と通導距離との関係から，単位通導距離当たりの葉面積ベースの主軸の水分通導性が陽樹冠のシュート内では一定であり，陰樹冠のシュート内では通導距離の影響がほとんどないことを明らかにした．また，単位葉面積あたりの葉柄の水分通導抵抗は主軸に比較して大きかった．特に陽樹冠のシュートでは全シュートの通導抵抗における葉柄の通導抵抗の割合が約90％を占めており，葉の水分特性やガス交換特性との関連性が示唆された．この結果は，葉柄の抵抗がシュート内での水分通導の規制要因となっていることを示しており，特に蒸散要求度の商い陽樹冠では，シュートの全体の致死的な水分損失を回避する上で重要な役割を果たすと考えられた．show more
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