The Relationship Between Environmental Factors and Behaviour of Stomata in the Rice Plant : 4. The relation between stomatal aperture and photosynthetic rate

Abstract

In a previous report⁹⁾ it was made clear that the stomata of leaf blade of rice plants closed to a considerable extent in fine days due to the unbalance of water economy in plant even when they grew in submerged paddy field with negligible influence of water potential surrounding the roots. For this time an investigation was undertaken to clarify the relation between stomatal aperture and photosynthetic rate of intact leaves outdoors under natural daylight with concomitant measurement of stomatal aperture by infiltration method. At first, the method to pursue the relation above mentioned was established by measuring the variation of photosynthetic rate of leaf blades from the beginning of measurement 1) in leaf blades with open stomata by the pretreatment of wrapping with polyethylene bags in light condition, 2) in ones with no pretreatment and 3) in ones with closed stomata by dark pretreatment. High correlation was, indeed, found between stomatal apetrture and photosythetic rate, the wider the former, the larger the latter. This relationship was not affected by the different stage of development or by leaf age. The photosynthetic activity of flag leaf, especially with small stomatal aperture, was larger than other leaves in equal stomatal aperture. In low light intensity, the photosynthetic rate stopped to increase above definite stomatal aperture, and the photosynthetic rate in equal stomatal aperture was smaller in leaf blades with lower nitrogen content than in ones with higher one, this difference becoming prominent in wider stomatal opening. From the results above mentioned it was suggested that the photosynthetic rate of rice plants grown in submerged paddy field was highly affected by stomatal aperture, reinforced by high light intensity and high nitrogen content of leaves.