Abstract
Using phytotrons with natural light, several day air-temperatures (night air-temperatures were 5°C lower than the respective day air-temperatures) were combined with the three soil-temperatures as shown in Table 5, to investigate the combined effects of air-and soil-temperatures on the growth and tuber production of the potato plants. The first treatment was given from juvenile to tuber formation stages for 23 days and the second treatment during bulking stage for 30 days. The results are summarized as follows : 1. The plant height was greatest at 24°C air-temperature (mean daily temperature; 21.5°C) combined with 30° soil-temperature; i.e. 24°-30°. Before tuberization occurred, the dry weight of whole plant almost parallelled plant height in response to various temperatures. Tuberization occurred most quickly at 24°-24°, being followed by 17°-17°. Under 30° air-temperature (mean daily temperature; 27°) tuberization was inhibited but slightly occurred when soil-temperature was lowered. At bulking stage, 17° air-temperature (mean daily temperature; 14.5°) was most favorable for tuber growth, and tuber yield was highest at 17°-17°, being followed by 24°-24°. 2. The dry matter and nitrogen distribution in leaf before tuberization were increased with decrease of air-temperature reaching more than 50% of whole plant. At bulking stage, however, they decreased at all organs except tubers with decrease of air-temperature due to their higher distributions at tubers. Under these situations, dry matter, total available carbohydrate (TAC) and total nitrogen or crude protein (CP) distributions at stem markedly decreased. 3. Leaf/stem in terms of dry matter and nitrogen accumulations increased with decrease of temperature, and tended to increase at soil-temperatures that promoted tuber growth. 4. Nitrogen concentrations and soluble-N/protein-N in leaf at bulking stage tended to decrease, while TAC concentrations, TAC/CP increased with decrase of air-temperatures. Stem and roots showed the almost similar responses. It was observed that soluble-N/protein-N in stem was especially higher as compared to other organs. In stem, CP concentrations were high under high air-temperature and low at the soil temperatures favorable for tuber growth, while TAC concentrations, sugar/starch, and TAC/CP increased with decrease of air-temperature, the latter being distinctly high at soil temperatures favorable for tuber growth. 5. The thickness of leaf blade and the length of palisade cells increased, while the pallisade cell density decreased with decrease of air-temperature. 6. RGR had a strong positive correlation with NAR, both being higher at the conditions favorable for tuber growth with a higher distribution of dry matter to it. NAR showed a positive correlation with length and volume of pallisade cell, but a negative correlation with its density, and showed positive correlations with root efficiency. 7. In the temperature regimes of this experiment, tuber yield showed a negative correlation with the mean air-soil temperatures (air+soil/2 temperatures), and the highest yield was obtained at 24°-24°, 17°-17°, sllowing a possibility that soil temperature too should change diurnally. It was suggested that the temperature conditions most favorable for tuber growth increased the matter in tubers, root efficiencies, NAR and leaf/stem ratio, resulting in the highest dry matter production of whole plant.
