Relationship between Nitrogen Content in Leaf Blades and Photosynthetic Rate of Rice Plants with Reference ot Stomatal Aperture and Conductance

[摘要] It was clarified in the previous paper that a positive correlation existed between nitrogen content in leaf blades on the different position of the stem and stomatal aperture at different growth stages by using rice plants supplied with different nitrogen level. The aboye result suggested that the increase in stomatal aperture due to higher nitrogen content ln leaf blades affected the photosynthetic rate, considering a high positive correlation between stomatal aperture and photosynthetic rate. The present investigation was undertaken to examine the role of stomatal aperture and conductance on the increase of photosynthetic rate in relation to nitrogen content in leaf blades. The rice plants with different nitrogen content were prepared by additional application of ammonium sulfate to soils several days before the measurement of photosynthetic rate in gasmetric system by using infrared gas analyzer. Stomatal aperture and conductance on the same leaf blades used for the measurement of photosynthesis was measured by improved infiltration method and by diffusive resistance meter, respectively. The results obtained are as follows. A positive correlation was found between nitrogen content in leaf blades and photosynthetic rate, but the photosynthetic rate varied to some extent even in leaf blades with the same nitrogen content probably due to the difference of stomatal aperture and conductance. A high positive correlation was clarified between stomatal aperture or conductance and the photosynthetic rate in leaf blades with much wide range of nitrogen content. These results indicated that the photosynthetic rate increased due to the increase in the stomatal aperture and conductance in leaf blades with higher nitrogen content. Furthermore, a positive correlation was found between nitrogen content and photosynthetic rate in leaf blades with the same stomatal aperture and conductance only when the extent of stomatal opening was sufficient. The incline of the regression line in Fig. 3 and 7 was smaller compared with that in Flg. 1 and 5, respectively. That is, the increase in the photosynthetic rate due to the increase in nitrogen content was comparatively small in leaf blades with the same stomatal aperture and conductance. Mesophyll conductance was positively correlated with nitrogen content in leaf blades, especially with lower nitrogen content. From these results mentioned above, possible two fhctors are considered for increase in photosynthetic rate in relation to nitrogen content; the one is the increase in the chloroplast activity in CO2 fixation and the other, the decrease in the resistance to CO2 transfer from the atmosphere to mesophyll due to the increase in the stomatal aperture and conductance.

[学科分类] 农业科学（综合）