Growth of 1-year-old Pinus densiflora, Cryptomeria japonica and Chamaecyparis obtusa Seedlings under Artificial Shadings

アカマツ，スギ，ヒノキの1年生苗を5月16日から9月30日まで，相対日射量100，77，55，39，26，13％のもとで育て，被陰が上長生長，重量生長にあたえる影響をしらべた。被陰がつよくなるほど重量生長は低下するが，その理由についてRGR，NAR，LWRや，光合成生産の面からの検討をこころみた。被陰による重量生長の低下は，地上部より地下部でいちじるしいので，被陰区の苗はT/R率が高い。被陰によってRGRが低下するが，それは主としてNARの低下，すなわち光不足による光合成生産の低下によるものである。相対日射量13％の被陰区での光合成生産の日補償点は，対照区（裸地）の日射量で，アカマツ400，スギ350，ヒノキ330g cal・cm－2・day－1である。処理期間中に日補償点に達しなかった日が，アカマツで61，スギで51，ヒノキで47日間あったと推定される。To study the effects of shading on growth among the different tree species, 1-year-old Pinus densiflora, Cryptomeria japonica and Chamaecyparis obtusa seedlings were grown under the six different light conditions, 100, 77, 55, 39, 26, and 13% in relative radiation intensity, respectively, for the periods May 16 to September 30, 1962 and 1963. The growth in dry weight decreased with shading, and the RGR, NAR, LWR, and photosynthetic production rate in the shaded plots were compared with those in the open plots. The decrease in dry weight growth with shading was remarkable in the root as compared with in the top, and the top root ratio was higher in the seedlings of the shaded plots. The depression in RGR in the shaded plots was mainly caused by the depression in NAR, that is, by the reduction in photosynthesis rate under the shadings. The daily light compensation points in photosynthetic production in the shading plot of 13% in relative radiation intensity were 400g cal・cm-2・day-1 of radiation intensity in the open in P. densiflora, 350 in Cr. japonica, and 330 in Ch. obtusa, respectively. The days below these compensation points were estimated to amount to 61 days in P. densiflora, 51 days in Cr. japonica, and 47 days in Ch. obtusa during the shading period, respectively