Distribution Ratio of Net Photosynthate to Photosynthetic and Non-Photosynthetic Systems in Shaded Plants

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Abstract
A method how to assess the distribution ratio of net photosynthate was mathematically derived and adopted in an analysis of shading effect on photosynthate distribution in Fagopyrum esculentum, Helianthus annuus, Vicia faba, Phaseolus aureus and Cryptotaenia canadensis var. japonica. 1. In general, photosynthetic system (F) increases its dry weight proportionally to individual plant weight (W) in the initial growth stage, but it decreases its growth rate with progressing W growth. This was formulated as F=μW/(1+νW), where μ and ν are constants. Then, the distribution ratio (δ=dF/dW) of photosynthate to F was derived as δ=μ/(1+νW)2. 2. As to the plant growth in the shading experiments μ and ν were obtained by using the C-D rule24), and the δ-W relation was derived from the above formula. In Ph. Aureus δ was independent of W, and in the other species it decreased with increasing W. The depression of δ with shading was evident in F. esculentum, H. annuus and V. faba. A shade plant, C. canadensis var. japonica has the highest δ values in the 75% light and its δ values were hardly depressed with shading. The trend of change of the distribution ratio with increasing W and shading can indicate nicely the shade tolerability of plants.

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