８月下旬に植栽したスギコンテナ苗の植栽当初の蒸散速度と成長

コンテナ苗は，根系発達が制約を受け，キャビティの形状に固まった根系となるために植栽地の土壌と根の接触が限られることが，植栽当初の根から葉への水分供給の制約要因となる可能性がある。本研究では，そのような特徴を有するスギコンテナ苗を用いた造林技術開発のための基礎的な知見を得ることを目的に，翌春の成長開始時までに土壌中への根系の発達によって根から葉への水分供給態勢を整えることが可能な８月下旬に植栽することの翌春からの成長への効果を調べた。８月下旬に植栽試験を開始し，植栽当初の蒸散・光合成速度と翌春からの成長を測定した。植栽当初のコンテナ苗の蒸散速度は，同時期に植栽した裸苗に比べて有意に高く，根系の吸水能が高く維持されていることが示された。コンテナ苗は，翌春までに有意に形状比が低下し，５月から旺盛な伸長成長を示すことが明らかになった。コンテナ苗の高さは，植栽時の２９±４cmから１１月には８５±２０cmになった。

Yukako Sugihara, Takeshi Tange：Transpiration rate and growth of containerised sugi (Cryptomeria japonica)seedlings planted in late August. Japanese Journal of Forest Environment 58:25―28, 2016.
Root system of a containerized seedling is restrained from natural development due to the limited volume of the cavity.The form of the root system can be a limiting factor for water supply from roots to leaves because of low connection betweenroot and soil. In the present study, we ran a planting trial of the containerized Cryptomeria japonica seedlings in lateAugust. We selected the planting season in order to allow the planted seedlings to grow the roots to prepare for the nextgrowing season. The seedlings were planted in late August. The transpiration and net photosynthetic rates were measuredfive times during two months after planting. We also measured the growth of shoot and root-collar diameter until the nextNovember. The transpiration rates of the containerized seedlings just after planting were significantly higher than those ofthe bare root seedlings which were planted at the same time. This result suggested that the roots of the containerized seedlingsmaintained the water absorption ability even just after planting. The H/D ratio of the containerized seedlings decreasedby next April and showed significant height growth from May. The height of the containerized seedlings increasedfrom 29 ± 4 cm at planting to 85 ± 20 cm during the growing season until the next November.