Abstract:

To investigate the response patterns of photosynthetic characteristics, chlorophyll fluorescence parameters, and yield of super hybrid rice leaves to nitrogen (N) application rate and planting density, this study used the hybrid indica rice Yixiangyou 2115 as experimental material and adopted a split-plot design with planting density as the main plot factor and N application rate as the subplot factor. Four levels of planting density were set: 125 300 hills/hm², 166 700 hills/hm², 200 800 hills/hm², and 250 600 hills/hm². Similarly, four levels of nitrogen application rate were established: 0 kg/hm², 75 kg/hm², 150 kg/hm², and 225 kg/hm². The results showed that in terms of photosynthetic characteristics, with the increase in nitrogen application rate, the net photosynthetic rate (Pn) and stomatal conductance (Gs) of rice both exhibited a gradually rising trend, while the intercellular CO₂ concentration (Ci) showed an opposite trend. As the planting density increased, Pn, Gs, and transpiration rate (Tr) all demonstrated a trend of first increasing and then decreasing. Regarding chlorophyll fluorescence characteristics, with the increase in nitrogen application rate, the maximum photosynthetic quantum yield of PSⅡ (Fv/Fm), photochemical quenching coefficient (qP), non-photochemical quenching coefficient (qN), and quantum yield of regulated energy dissipation [Y(NPQ)] all showed a trend of first rising and then falling, while the actual photosynthetic quantum yield of PSⅡ [Y(II)], apparent electron transport rate (ETR), and quantum yield of non-regulated energy dissipation [Y(NO)] exhibited the opposite trend. As the planting density increased, Fv/Fm, Y(Ⅱ), ETR, qP, and qN all showed a trend of first increasing and then decreasing. In terms of yield, with the increase in nitrogen application rate, rice yield showed a trend of first increasing and then decreasing, with a turning point at 150 kg/hm² of nitrogen application rate. Similarly, as the planting density increased, rice yield also showed a trend of first increasing and then decreasing. Under the experimental conditions, the suitable nitrogen application rate for Yixiangyou 2115 was 150 kg/hm² and the suitable planting density was 200 800 hills/hm², at which the rice yield could reach 9 267.55 kg/hm². Further calculations using regression equations revealed that the optimal nitrogen application rate was 155.00 kg/hm² and the optimal planting density was 191 300 hills/hm², under which the highest yield of 9 384.64 kg/hm² could be achieved. In conclusion, moderate nitrogen application and medium planting density can enhance the light adaptation ability of super hybrid indica rice leaves, improve their photosynthetic rate and efficiency, and help optimize yield components, thereby achieving high rice yield.

Key words: hybrid indica rice, nitrogen application rate, planting density, photosynthetic characteristics, fluorescence parameters, yield

摘要：

为探明施氮量与种植密度对超级稻叶片光合特性、叶绿素荧光参数以及产量的影响，以杂交籼稻宜香优2115为试验材料，采用以种植密度为主区、施氮量为副区的两因素裂区设计开展试验。种植密度设置4个水平，分别为12.53万穴/hm²、16.67万穴/hm²、20.08万穴/hm²和25.06万穴/hm²；施氮量同样设置4个水平，即0 kg/hm²、75 kg/hm²、150 kg/hm²和225 kg/hm²。结果显示，在光合特性方面，随着施氮量的增加，水稻的净光合速率（Pn）和气孔导度（Gs）均呈现出逐渐上升的趋势，而胞间二氧化碳浓度（Ci）则表现出相反的变化趋势；随着种植密度的增大，Pn、Gs以及Tr（蒸腾速率）均呈现先升高后降低的趋势。在叶绿素荧光特性方面，随着施氮量的提升，PSⅡ最大光合量子产量（Fv/Fm）、光化学淬灭系数（qP）、非光化学淬灭系数（qN）以及调节性能量耗散量子产量[Y(NPQ)]均呈现先上升后下降的趋势，而PSⅡ实际光合量子产量[Y(Ⅱ)]、表观电子传递速率（ETR）和非调节性能量耗散量子产量[Y(NO)]的变化趋势则与之相反；随着种植密度的增加，Fv/Fm、Y(Ⅱ)、ETR、qP、qN均表现为先升高后降低。随着施氮量的增加和种植密度的增大，水稻产量均呈现先上升后下降的趋势，施氮量转折点为150 kg/hm²。在本试验条件下，宜香优2115较为适宜的氮肥施用量为150 kg/hm²、种植密度为20.08万穴/hm²，此条件下水稻产量可达9 267.55 kg/hm²。通过回归方程计算进一步得出，最佳施氮量为155.00 kg/hm²、最佳种植密度为19.13万穴/hm²，在此条件下可获得最高产量9 384.64 kg/hm²。综上所述，中氮水平与中等种植密度的条件，既能够增强超级杂交籼稻叶片对光的适应能力，提高其光合速率与光合效率，又有助于优化产量构成因子，从而实现水稻高产。

关键词: 杂交籼稻, 施氮量, 种植密度, 光合特性, 荧光参数, 产量