Relationship between Nitrogen Content in Leaf Blades and Photosynthetic Rate in Rice Plants Measured with an Infrared Gas Analyzer and on Oxygen Electrode

[摘要] It was suggested in the previous paper that the photosynthetic rate in leaf blades with higher nitrogen content increased not only due to the increase in chloroplast activity in CO2 fixation, but also due to the decrease in the resistance of CO2 transfer from atmosphere to mesophyll in relation to the increase in stomatal aperture and conductance. The present investigation was undertaken to ascertain the above suggestion by comparing between the photosynthetic rate measured with the infrared gas analyzer and that measured with the oxygen electrode. The photosynthetic rate in gasmetric system is much affected by stomatal aperture and conductance, while it is considered that the photosynthetic rate in liquid substrate is little affected by stomatal resistance on CO2 absorption in mesophyll because CO2 is absorbed mainly through the cut surface of the leaf slice. The photosynthetic rate, diffusive conductance and stomatal aperture in gasmetric system were positively and closely correlated with nitrogen content in leaf blades. A high positive correlation was found between diffusive conductance or stomatal aperture and photosynthetic rate in leaf blades with wide range of nitrogen content. These results indicate that the photosynthetic rate increased due to the increase in the diffusive conductance and stomatal aperture in leaf blades with higher nitrogen content as reported in the previous paper. The photosynthetic rate in the substrate with the concentration of 20 mM NaHCO3 was positively correlated with nitrogen content in leaf blades. The increase of nitrogen content in leaf blades from 7.1 to 19.1 mg/dm2 increased in the photosynthetic rate measured with the infrared gas analyzer by 2.5 times, while it increased in the photosynthetic rate measured with the oxygen electrode by 2.0 times. To examine the obtained data in detail the increase in the photosynthetic rate was compared in leaf blades on the same position of the stem. The incline of regression lines of the data measured with the gas analyzer were much larger in 2nd, 3rd and 4th leaf from the first expanded leaf, compared with those measured with the oxygen electrode. It is suggested that the difference between the incline of the two regression lines of the same leaf position indicated the influence of the stomatal aperture and diffusive conductance on the increase in photosynthetic rate with the increase in nitrogen content in leaf blades.

[学科分类] 农业科学（综合）