Studies on the Relationship between Photosynthesis and Varietal Adaptablity for Heavy Manuring in Rice Plant : II. The relationship in the case of early-maturing varieties

摘要

In six early-maturing rice varieties, Fujiminori (suitable for heavy manuring), Fujisaka No. 5 (suitable), Akibae (a little suitable), Norin No. 1 (less suitable), Obanazawa No. 1 (least suitable), and Kamenoo (least suitable), which were cultured on the paddy field under normal and double nitrogen levels, it was shown that the ratio of photosynthetic capacity to respiration (P/R), both on field area basis, had an intimate relationship with the adaptability for heavy manuring, the more suitable the higher the ratio. This is in good accordance with our previous results on medium varieties. Moreover, the following facts were observed by investigating the four factors which compose the P/R ratio: (1) Photosynthetic activity on unit leaf area was higher in the varieties less suitable for heavy manuring, just reverse to the case of medium varieties. However, (2) respiration rate of unit dry matter was higher in less suitable varieties in accordance with medium varieties. (3) While the plant shape of less suitable varieties under normal nitrogen supply was rather unfavorable for receiving light efficiently in comparison to suitable ones, it became comparatively favorable under heavy nitrogen supply, considering its greater increase in total leaf area. (4) There was no definite relationship found between LAR and the adaptability. From these it was deduced that the above-mentioned changes in the ratio brought about by heavy nitrogen supply were chiefly caused by changes in the second factor, namely the respiratory activity. Summing up the results of both early and medium varieties, it may be concluded as follows: In both maturing varieties, from the view point of efficiency in dry matter production, the varietal adaptability in rice for heavy manuring has a close relationship with the P/R ratio which represents a composite efficiency in dry matter production of rice plants as a whole. However, early and medium varieties showed the following differences in the relationship: In medium varieties, the adaptability had a correlation with the P/R ratio not in its absolute value but in its rate of change due to high nitrogen supply, whereas in early varieties, the correlation was seen regardless of the level of nitrogen supply. In the case of early varieties, therefore, it is not the "adaptability for heavy manuring" itself but the "high yielding ability" that has a substantial correlation with the varietal response for manuring. When the grain yield is considered from two phases, namely dry matter production and its translocation, it may be said that in medium varieties, the P/R ratio is directly associated with the "adaptability" in the former phase, whereas in early varieties, it has a relationship with the "adaptability" only in broader meaning similar to the "high yielding ability". It may be possible, therefore, that in early varieties a definite relationship is to be found in the latter phase, namely in the translocation phase, between physiological characteristics and the "adaptability for heavy manuring".