| 概要 |
移植にともなう樹木の通水抵抗の変化を，ヒノキ，クロマツおよびタブノキの3樹種について比較した．根鉢径を5cm，20cmとして移植した苗の日中の単位葉面積あたりの蒸散速度(Tr),梢端部の木部圧ポテンシャル(Ψleaf)，地際部の木部圧ポテンシャル(Ψstem),および明け方の葉の木部圧ポテンシャル(BP)を移植直前から移植後2週間目まで測定し，これらの値から単位葉面積あたりの通水抵抗(Rt)と地下...部抵抗の割合(Rr/Rt)を算出した．なお，Ψstemは直接測定できなかったのでBagged-Shoot法を用いて推定した．測定期間中の対照木のRtとRr/Rtは変化せずほぼ一定であったが，移植木のRt,Rr/Rtは移植直後にともに増加した．クロマツとタブノキのRtの増加は急激で移植直後に対照木の30倍から120倍となり，Rr/Rtも0.9以上で移植1週間以内で鉢径にかかわらず蒸散は停止した．これに対し，ヒノキのRtおよびRr/Rtは緩やかに増大した．5cm処理ほ移植1週間後まで徐々に増加し,Rtが対照木の250倍,Rr/Rtが0．9に達したのちに蒸散を停止した．20cm処理には蒸散の停止は認められず，移植2週間後のRは対照木の70倍,地下部の割合は0．9であった．対照木のBPは測定期間中を通してほとんど変化しなかったが，移植木のBPはRtの変化と同様にクロマツとタブノキでは急激に低下し，ヒノキでは緩やかに低下した．翌春まで生残したヒノキの20cm処理のRtは低下し，Rr/Rtも小さくなったが，対照木までの回復は認められず夏期に向かって再びRtの増加が認められた．このように移植により通水拡抗は増加したが，その大きな原因は根の通水抵抗の増加であることが示され，さらに活着木においては根の通水抵抗の回復が確認された．また，抵抗の変化には根鉢径と樹種による差が認められたが，その要因として鉢内の根量を規定する根の分岐形態などの種特性が関与していると予想された．
Changes in the hydraulic resistance were compared among Chumecyparis oblusa, Pinus thunbergii and Persea thunbergii transplanted trees. The hydraulic resistance per unit leai area ( Rt), proportion of root hydraulic resistance to total resistance (Rr/Rt) and predawn leai xylenl pressure potential (BP) of transplanted trees with 390 cm3 (SRB; small root ball) and 25000 cm3 (LRB; large root ball) root balls volume were observed from just before transplanting until two weelrs after. The Rt, Rr/Rt, and BP of control trees did not show remarltable changes throughout measurement. Eight days after transplanting, the Rt of SRB treated Chamczcyparis had reached 250 times as large as control tree, and transpiration ceased. The Rr/Rt increased to 0.97, two weeks after. Under LRB treated Chamecyparis, the cessation of transpiration was not recognized. The Rt increased to 70 times as large as control, and Rr/Rt was 0.93, two weeks after. The BP of SRB and LRB treated Chamecyparis, gradually declined to -2.0MPa and -0.8MPa, respectively. Under the Pinus and Persea transplanted trees, the Rt increased to 30-120 times as large as control trees, and the Rr/Rt were over 0.9 just after transplanting. Furthermore, Tr ceased within one weelt after transplanting in both of the root treatments. Thc BP in transplanted trees declined immediately, similar to the Rt trends. The LRB treated Chamaecyparis tree survived until next spring, but the Rt and Rr/Rt did not return to the levels under control tree. With this, increment of root hydraulic resistance was considered a major reason for the rapid increase of hydraulic resistance in transplanted trees. There were also dilferent trends in the changes in hydraulic resistance, depending on the root ball volume and tree species. Species specific characteristics, like thc root branching structure, root volume regulation in root ball, may account for the difference.続きを見る
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Mendeley出力
