抄録
Photosynthesis is the most important factor in dry matter production. Therefore, as the first step to acquire fundamental knowledge about the photosynthesis of sweet potato, several experiments were undertaken with individual leaf. Apparent photosynthetic rates of intact leaves were measured under-natural conditions by the use of the apparatus shown in Fig. 1. As experimental materials, some varieties of sweet potato were grown in field and in Wagner's pots under different applications of fertilizer. The following results were obtained: 1) Light saturation values measured on a horizontal surface with a intact leaf and a detached leaf were about 30 k lux. Light saturation values of the population were, however, higher than that of individual leaf owing to the lowering of light intensity caused by mutual shading of leaves in the population. Maximum values of photosynthetic rates were about 20 mg CO2/100 cm2/hr as mean value and they were not different significantly among four varieties. 2) The relation between the photosynthetic rate of leaves and nitrogen, phosphorus and potassium concentrations on dry weight basis in them was investigated with intact leaves of Norin No. 1 which include various ages except young leaves below 15 leaf position, under different manurial conditions. It was observed that potassium exerted a much larger effect on photosynthetic rates than nitrogen. Leaves which contained more. than 4 per cent potassium showed a very high photosynthetic ability even when nitrogen level was as low as 2.2 per cent. On the other hand, the photosynthetic ability was low when nitrogen ranged above 3 per cent but potassium was below 4 per cent. The young leaves below 15 days old showed, however, high ability of the photosynthesis in spite of the same level of potassium and nitrogen as older leaves (Fig. 5). There was no statistical interaction between the phosphorus per cent and photosynthetic rates in leaves.
