1978 Volume 47 Issue 2 Pages 336-343
In the previous paper, the conversion efficiencies (Eφeff) of photosynthetically active radiation (PhAR) in net photosynthesis of rice and soybean plant population were reported. In the present paper, with an object to estimate the conversion efficiency (Eφeff(g)) of PhAR in gross photosynthesis of crop stands, attempts were made to detail the expression of respiration. For this purpose, in accordance with McCree's formula, respiration rate was divided into following two components, i.e. the maintenance and consutrctive respiration. The results obtained were as follows; 1. Dark respiration rates (maintenance and constructive respiration) per unit dry weight of soybean were higher than rice plant, especially in leaf and fruit (ears or pods) (fig. 1). 2. Dark respiration rates of rice plant population (per unit ground area) were higher than soybean population, in spite of lower respiration rate per unit dry weight in rice. That was caused by the fact that the dry weight per ground area of rice plant population were higher than soybean (table 2). 3. As both of the conversion efficiency (Eφeff) in net photosynthesis and dark respiration rate R of rice plant population were higher than soybean population, the conversion efficiency (Eφeff(g)) in gross photosynthesis of rice were higher than soybean. Eφeff(g) were 5.35-12.74% and 4.18-9.14% for rice and soybean plant, respectively (table 3). 4. Maintenance coefficients m were found almost same in both plants but the maintenance respiration rate Rm of rice were always higher than soybean (table 5). The maintenance respiration rate Rm of crop population increased with accumulation of dry matter, and it exceeded more than a half of dark respiration rate (table 5). Therefore, it would be desirable for the crop to have lower maintenance coefficient for saving loss of dry matter in maintenance respiration. 5. Despite very little difference in dry matter production efficiency Yg and maintenance coefficient m between rice and soybean plant population, there was a clear difference in Eφeff(g) in gross photosynthesis. Those must be caused by the fact that the absorbed energy needed for unit gross photosynthetic production was different in both crop stands (table 5).
