Studies on the growth control of pine species under the day-length in Okinawa (II)(Forestry Experiment Station)

沖縄地方におけるアカマツ, クロマツの生育不良の原因を, 日長の面から検討し, それらの樹種の栄養生長と日長との関係について調査した。1.本研究は, 沖縄の自然日長区と, それらの樹種の天然分布のほぼ中央部となる京都地方の自然日長になるように, 自然日長に日没から2時間人工補光した区を設定し, 処理区別に種々の形質について比較した。2.幹, 葉の伸長生長は補光区で著しく増大し, 自然日長区で減少した。乾重量では, とくに全葉重量に大きな違いがみられ, 補光区は, 自然日長区の約2倍になった。3.幹の節間長, 針葉の大きさは補光区で明らかに増大した。4.同化部重と非同化部重の関係から, 補光区は自然日長区に比べ, 相対的に同化部重が増大した。これらのことから, アカマツ, クロマツの天然分布域と導入地域である沖縄地方における生育の違いは, 日長がその一因として関与していることが明らかとなった。Pinus densiflora and Pinus thunbergii are widely distribute from Honshu to Kyushu in Japan. In the Okinawa Islands, however, it is observed that these species clearly decrease growth and development of planted the seedlings. This paper deals with response on the vegetative growth of 2-years-old seedlings of Pinus densiflora and Pinus thunbergii under two conditions of day length. 1. the seedlings were only bred under natural day light from sunrise to sunset (represent by ND) in about 4 monthes after 18th Feb. 1976. Other seedlings were bred under the same natural day light and complemented illumination after sunset by incandescent lamps in two hours(LD). The light intensity of complementary illumination was approximately 200 lux on the growing point of seedlings. In day-length of LD treatment is approximately the same length in Kyoto which is equivalent to the central area of the distributed range of these species. 2. The elongation of stem and needles under LD treatment was remarkably larger than those organs under ND treatment. The dry weight of needles affected strikingly under photoperiodic treatment and the total dry weight of needles under LD treatment was about twice as much as that under ND treatment. 3. The internode-length in stem and length of a needle of the seedlings bred under LD treatment was greater than those under ND treatment. 4. It was clear that LD treatment predominantly increased the dry weight of needles from the allometric relations between dry weight of needles and dry weight of stem and branches. The above results obtained were concluded as follows; it was shown that Pinus densiflora and Pinus thunbergii bred in the Okinawa islands were evidently inhibited by natural day-length which was a factor into all environmental factors