Height and dry-weigt growth in yearlings of <i>Pinus densiflora</i> grown under various light break treatment

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  • 種々の光中断処理のもとで育てた当年生アカマツの伸長ならびに乾物重量成長
  • 種々の光中断処理のもとで育てた当年生アカマツの伸長ならびに乾物重量生長
  • シュジュ ノ ヒカリ チュウダン ショリ ノ モト デ ソダテタ トウネンセイ

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During the period from May 15, when the yearlings of Pinus densiflora fully expanded their cotyledons, to October 9, the yearlings were grown under various photoperiodic conditions as follows. The yearlings grown under natural day light for 7 hours (9:00 a.m._??_4:00 p.m.) a day were transferred to a dark room and illuminated by artificial light of about 50lux light-intensity for one hour at various times in a daily dark period. The longest continuous dark period in a day was 16 hours, and was 12 hours in the cases of light break A and B, 8 hours for light break C, 5 hours for light break D, and O hour where the yearlings were subjected to 24 hours of light (7 hours of natural light and 17 hours of artificial light). The height and dry-weight of the tops in the yearlings increased in proportion to the length of daily continuous dark period, but the height and dry-weight of the roots were scarcely affected. In the tops, the shorter the length of daily continuous dark period was, the greater the height of axial stem, number, length and dry-weight of leaves (both of primary and secondary ones) were. Also, the number of individuals with secondary leaves, and the length of internode in axial stem increased, but not the dry-weight of the axial stem including hypocotyl. Therefore, it seemed that the growth and development of the leaves were largely affected by the length of continuous dark period in a day.

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