Effect of Light Intensity and Planting Density on the Growth of <i>Cryptomeria japonica</i> Seedlings

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  • スギ苗の生長に及ぼす光の強さと植栽密度の影響
  • スギ ナエ ノ セイチョウ ニ オヨボス ヒカリ ノ ツヨサ ト ショクサイミツド ノ エイキョウ

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Abstract

To make clear the effect of light intensity and planting density on the growth of Cryplomeria japonica seedlings, experiment was made under 24 different combinations of light intensity and planting density. One-year old seedlings were shaded at 100, 76, 59, 47, 37 and 30% of full light, and planted at 25, 59.2, 123.5 and 277.8 no/m2 planting densities. After one growing season, the stems, roots and leaves were measured.<br> The results were as follows:<br> 1) The weight of average individuals decreased and the amount of standing crops per unit area increased with increasing planting density at each light intensity level. Also, at each planting density, it seems that optimum curves were figured for the relation between the weight of average individuals or standing crops and the light intensity.<br> 2) The net production affected by light intensity and planting density was the same as in the case of standing crops. The largest value of net production in shaded light treatment was 14.5 t/ha•yr, and this value was larger than the largest value 10.5 t/ha•yr obtained in 100% light treatment. The amount of annual product of leaves was 3.1_??_6.1 t/ha•yr in 100% light intensity treatment and these were nearly equal to that of younger or middle-aged stands, but in shaded light and high density treatment, the amount of annual product of leaves were 7.5_??_9.5 t/ha•yr.<br> 3) It was recognized that planting density is reciprocal factor and light intensity is optimum factor in the logistic theory of plant growth. So, we examined adaptation of the following reciprocal equation shown by HOZUMI:<br> _??_<br> where, w is the average individual weight, ρ is planting density, L is light intensity and A1, A2, A2', A12, A12' and B are constants. The relative errors of observed values and calculated values were about 20%. The optimum light intensity (Lopt) varied by planting density, so the relation between the optimum light intensity and planting density adopted following equation:<br> _??_ <br> The optimum light intensity was about 60% in the case of ρ→0 and 83% in ρ→∞.

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