Effect of Potassium on Dynamic Aspects of Photosynthesis and Yield Formation of Hybrid Rice Plants

Pot experiment was carried out on semihydrogenic soil of low potassium content. Each pot filled with 15 kg soil with 2.25 g N as urea, 1.50 g P_2O_5 as superphosphate and three levels of K as potassium chloride: K_0(O), K_1(1.5g K/pot) and K_2(3.0gK/pot). All fertilizers were used as basal dressing. The results are summerized as follows: 1) Deficiency of K decreased net photosynthetic rate and increased dark respiratory rate of the leaf in whole developmental course, photosynthetic area and duration of photosynthetic function were also reduced, with poor growth of hybrid rice plants. It was evident that net photosynthetic rate increased, duration of photosynthetic function prolonged and dark respiratory rate maintained a lower level in K treatment. 2) The chloroplast of K_0 treatment was developed slowly but destructed quickly, while it was changed to converse state by K treatment. 3) In the filling stage, the net photosynthetic rate of K_0 treatment showed significant midday depression, while K_1 and K_2 treatment showed in steady state. The midday depression of photosynthesis, causing a decrease of net photosynthetic rate was related to the high rate of transpiration with a peak at 9 AM, and 'the higher loss of water. 4) K content in leaves of K_0 treatment showed a clear gradient from top downward. The data of lower leaves contained only 30.08% of flag Ieaves at filling stage. Due to the lower K content in leaves, the rice plants showed senescence and poor growth of roots. K content in leaves of K_1 and K_2 showed no clear gradient from top downward. 5) Potassium nutrition increased photosynthetic area, photosynthetic duration, number of grains and grain yield.