Studies on Matter Production of Taro Plant (Colocasia esculenta SCHOTT) : I. Changes with growth in photosynthetic rate of single leaf

Abstract

Photosynthetic ability of taro plant was investigated with an early variety, Ishikawa-wase, growing in pot. Photosynthetic rate of each single leaf was measured using the assimilation chamber as shown Fig. 1 for intact leaves. The results obtained were as follows: 1. Leaves developed successively with a time interval of several days. Total number of leaves in whole growing period showed 16-18. Life of the leaf differed with the leaf position. Duration from unfolding to withering was 40-45 days for lower leaves in early stage of growth and 55-80 days for upper leaves in later stage of that. There was large difference in leaf area among leaf positions. The higher the position of leat the larger the leaf area, excepting that a few leaves of uppermost position showed rather small leaf area. 2. Photosynthetic rate of each single leaf increased in new expanding leaf and reached a high level 14 or 15 days after expansion. It maintained the high level for about 10 days and, after that, declined gradually with aging. Thus, photosynthetic rate of single leaf varied with the leaf age. 3. The maximum rate of photosynthesis of single leaf under the conditions of light saturations was 30-35 mg CO2/dm2/hr for lower leaves and about 20 mg CO2 for middle and upper leaves. The light saturation point was about 70 Klx of radiation for younger leaves and 20-30 Klx for older leaves. 4. Optimum temperature for apparent photosynthesis of single leaf was approximately 30°C, while the photosynthetic rate did not show marked differences within the temperature from 22° to 35°C. 5. Temperature coefficient of dark respiration (O10) calculated was 2.05 for younger leaf and 1.62 for older leaf. Therefore, effect of temperature on respiratory activity differed with leaf age. 6. There was large difference with leaf position in maximum rate of photosynthesis of whole leaf area, showing 200 mg CO2/leaf/hr or more for upper leaves. That was due to the difference of leaf area of the position. Total value of maximum rate of photosynthesis accumulated for all of the leaves existing at the time of measurement showed marked increase from end of June, and it did not show the decline even in late September.