Abstract: 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 P₂O₅ as superphosphate and three levels of K as potassium chloride: K₀(O), K₁(1.5g K/pot) and K₂(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 K₀ 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 K₀ treatment showed significant midday depression, while K₁ and K₂ 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 K₀ 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 K₁ and K₂ showed no clear gradient from top downward. 5) Potassium nutrition increased photosynthetic area, photosynthetic duration, number of grains and grain yield.

Key words: Potassium nutrition, Hybrid rice, Photosynthesis, Dark respiration, Transpiration rate, Yield formation

摘要： 用杂交稻威优35号在低钾土壤上进行盆栽试验，设置三个钾水平：K0(不施钾)；K1(1．5 g K/ 15 kg土)；K2(3．0 g K／15 kg土)。结果表明：(1) K0处理叶片发育过程中净光合率降低而暗呼吸增高，叶绿体发育迟缓而解体较早，光合功能期缩短；K1及K2的净光合率明显高于K0，光合功能期亦较长，而暗呼吸则长时期保持较低水平。(2)K0处理在灌浆期净光合作用有明显的“午休”现象， 而K1、K2则在夏日中午仍保持较稳定的净光合率。(3) K0处理“午休”的出现与蒸腾速率增高有关，且在上午9时还有一蒸腾高峰，使叶子大量失水；施钾处理在一天中的蒸腾曲线则较平稳。(4)K0处理稻株叶片中含K量从上到下有明显梯度，灌浆期下层叶的含K量仅为剑叶的30．08％，易引起早衰，且使根系生长受到严重影响；施K处理叶片从上到下无明显梯度。总之，施K增加光合面积，避免早衰，增加粒数，显著提高谷粒产量。

关键词: 钾营养, 杂交稻, 光合作用, 暗呼吸, 蒸腾速率, 产量形成