光合作用是决定作物产量的重要因素，进行棉花光合日变化特性研究，对于探究棉花干物质积累规律和增产机理均有很大的指导意义。采用CB-1102型光合蒸腾作用测定系统，研究棉花花铃期光合指标的日变化规律。结果表明，净光合速率(Pn)的日变化曲线为光合日变化模式之一的双峰型，光合速率的峰值分别出现在10:00时和15:00时，13:00时左右出现午休现象。蒸腾速率的日变化规律呈双峰型，峰值出现在11:00时和15:00时左右。气孔导度(Cleaf)的日变化规律也呈双峰型曲线，峰值出现在10:00时（小峰值）和15:00时左右（大峰值）。胞间CO2浓度呈现斜“V”字型的日变化规律，12:00时为全天最低值。

Photosynthesis is the important factors for yield formation, research on Diurnal Variation of Photosynthesis have guiding value for exploration the Rule of dry matter accumulation and yield-increasing mechanism of cotton. With CB-1102 Portable Photosynthetic System, the photosynthetic rate of cotton leaf was studied at blossoming and boll forming stage. The results showed that daily changes of net photosynthetic rate presented a bimodal curve, peak value appeared at 10:00 and 15:00, midday depression appeared at 13:00; transpiration rate presented a bimodal curve, peak value appeared at 11:00 and 15:00; stomatal conductance presented a bimodal curve, peak value appeared at 10:00 (small) and 15:00 (maximum peak); Variation of intercellular CO2 concentration appeared “V” shape, lowest value appeared at 12:00.