1994 Volume 63 Issue 3 Pages 539-545
In order to verify the difference in diurnal changes in photosynthesis in rice plants with different root activities, the experiment was conducted with a control plant and a soluble starch-applied plant more than 16 days after soluble starch application. There was a larger difference in the diurnal changes in the photosynthesis and stomatal conductance, due to increase in Rubisco contents resulted from the application of soluble starch and nitrogen. Photosynthesis and stomatal conductance in the low-root activity plant were higher before 10 o'clock and lower at midday and in the afternoon. The response curves of the photosynthesis to photosynthetic photon flux (PPF) expressed a significant saturable curve and were obviously different between morning and afternoon under PPF over 1000 μmolm-2s-1. An obvious diurnal change in the initial activity and activation rate of Rubisco carboxylation had been found. They all were higher at midday than in the early morning and late afternoon. The initial activity based on leaf area was significantly higher in the low-root activity rice plant, but its activation rate was obviously lower. Therefore, the difference in diurnal changes in photosynthesis between the different root activity plants can not be attributed to the difference in Rubisco activity, but mainly to the difference of the midday drop in stomatal conductance, which was significantly correlative to photosynthesis.
