Studies on the Relationship between Photosynthesis and Varietal Adaptability for Heavy Manuring in Rice Plant : I. The relationship in the case of medium-maturing varieties

摘要

When rice plants are supplied with a large amount of fertilizer, especially of nitrogenous one, increase in grain yield is not always proportional to the amount of applied manure, the response being different from variety to variety. The fact has been explained as the difference in "varietal adaptability for heavy manuring". According to Baba, three different characteristics of rice plant, namely, resistance to disease (rice blast), resistance to lodging, and morphological and physiological characteristics, are concerned with this adaptability. On considering the third characteristics, which are believed to, be associated with the adaptability in narrower meaning, we meet with two fundamental problems of different category: The first is how the pattern of dry matter production will be influenced, and the second is what changes will be brought about in the distribution or translocation of the matter produced, under heavily manured conditions. It is regarding the first problem that we have intended to carry out a series of experiments, in which the meaturement of photosynthesis and respiration, both under field and laboratory conditions, and of other plant factors concerning the dry matter production in the field were included. The present paper reports the results of experiments using the following six, medium-maturing varieties which are different in their adaptability for heavy manuring: Hokuriku No. 52 (most suitable for heavy manuring), Norin No. 25 (suitable), Yamakogane (suitable), Kiyosumi (less suitable), Chiba-asahi (less suitable), and Tamanishiki (least suitable). These were cultured on the paddy field under normal and double nitrogen supply. The results obtained may be summarized as follows: (1) The rate of promotion in the photosynthetic capacity, on field area basis, of the heavily fertilized plot to the normally fertilized plot was greater in varieties more suitable for heavy manuring than in less suitable ones. However, the rate of promotion in respiration, also on field area basis, was greater in less suitable varieties. The ratio, therefore, of photosynthetic capacity to respiration rate (P/R), which may be regarded as an index of efficiency in dry matter production, was higher in more suitable varieties than less suitable ones, when nitrogen was abundantly supplied. (2) The P/R ratio can be analysed into four factors; photosynthetic activity of unit leaf area (p0), respiration rate of unit dry matter (r), light-receiving coefficient (f), and leaf area ratio (LAR), in the following way: As there exists the following equation among P, f, p0 and the total leaf area (A), according to our previous work (Murata et al., 1957), P=Afp0, the P/R ratio can be transformed into, P/R=fp0A/rW=fp0/r=A/W=fp0/rLAR where W and r stand for the total dry weight of the plant, and its per unit respiratory activity, respectively. Through almost all the varieties used, it was found that by increasing nitrogen supply those varieties suitable for heavy manuring were more promoted or improved in their unit photosynthetic activity, LAR, and efficiency in receiving light, but not so much in their unit respiration rate, as compared wtih less suitable varieties. It was concluded that the P/R ratio was determined by the composit effect of all these changes in the four factors and it was suggested that varieties more suitable for heavy manuring can produce dry matter more efficiently than less suitable ones in the field under heavy manuring.