切り取り前後の樹木の呼吸変化について

Abstract

樹木の呼吸量測定のための基礎的実験として, 主にスギ, オオシマザクラの鉢植え苗を用いて, 切り取り前後の葉, 幹, 枝, 細根の呼吸量の変化をしらべた。落葉広葉樹の葉では, 切り取り後3, 4時間内は切り取り前とほぼ同量の呼吸を続け, その後増大する。常緑樹の葉では, 7, 8時間または, 樹種によってはそれ以上の間, 呼吸に変化はみられない。切り取り後の葉の呼吸の増大は, 葉の乾燥と密接な関係がみられ, 急激な水分の蒸散に際しての異常呼吸であろうと考えられる。常緑樹の葉と落葉樹の葉のあいだの呼吸増大までの時間的経過における差異は, 両者の葉の構造の差にもとづく蒸散量の違いによるものであろうと推定される。幹, 枝の呼吸は, 切り取り後, 広葉樹では5 - 10時間内に外傷の影響があらわれ, 一時的な呼吸の増大を招くが, 再び減少し安定する。針葉樹では, 外傷の影響があらわれるのがかなり遅れる。幹, 枝, 根等での切り取りの影響は傷の大きさにも関係し, 傷面積が健全な部分に対して大きいほど呼吸量の増大現象が早くあらわれ, その増大量も大きい。傷面積の小さい細根等では, 外傷の影響はほとんど認められなかった。切り取った樹木の呼吸測定に際しては, 樹種, 樹体部分の切り取りによる呼吸への影響に注意を要し, 呼吸の増大以前に測定を終えることが望ましいと思われる。

The change in the rate of respiration of excised tree organs (leaves, stems, branches and fine roots) was studied. Rate of CO2 output was followed using an infrared gas analyzer (URAS). Four-year-old seedlings of Cryptomeria japonica and Prunus Lannesiana as well as other species were used. 1) Change in respiratory rate of the leaf after cutting. Within three or four hours after cutting, the respiration of leaves of deciduous broad-leaved trees remained normal. But, soon after that, the respiratory rate increased to a peak and then decreased. On the other hand, excised leaves of evergreen broad-leaved and coniferous trees maintained the normal level of respiration for a longer period than those of deciduous broad-leaved trees. The cause of the respiratory rise in the leaf may be different from that in the woody organ. In the case of the leaf this rise seemed to be caused by a rapid withering of the leaf. The difference in the pattern of change in the respiratory rate of the leaf between deciduous and evergreen trees would be ascribable to a difference in the structure of the leaf against withering. Measurement should be carried out within three or four hours after cutting, on the leaves of deciduous broad-leaved trees, and within seven or eight hours on those of evergreen trees. 2) Change in respiratory rate of the woody organ after cutting. Respiratory rate of the excised woody organ began to rise several hours after cutting, reached a maximum, soon declined and became stable at a level which was not the same as the initial. Reliable values, therefore, can be obtained only when measurement is carried out within the initial stable period. The duration of normal respiration before the start of the respiratory rise varied with the species of trees. The length of that duration in 20-cm stem sections was 5-10 hours for broad-leaved trees, and 3-4 days or more for coniferous trees. Such duration and maximal value in the respiratory rise, however, depended upon the magnitude of the wounded area of the section. With fine roots or branchlets, little or no effect of cutting was observed upon the respiratory rate of the excised sections.