Studies on the time Course of respiratory rate of mulberry leaves after putting out the illumination

Abstract

Mulberry leaves which had been illuminated more than 120 minutes were examined for the change in their resrespiratory rate after putting out the illumination.
The results are summarized as follows:
1. The respiratory rate depended on the order of leaf and the growth stage, especially the former. The difference concerning the growth stage was distinguished between the season before the eary September and the season after late September.
2. The respiratory rate was relatively high immediately after putting out the illumination and decreased rapidly to attain a settled level in 30 to 60 minutes. The settled level of respiratory rate may be regarded as the actual respiratory rate by night.
3. The proportion of the settled level of respiratory rate to the rate measured immediately after putting out the illumination was about 60 percent, approximately 50 percent and 70 to 80 percent for young immature, mature and senescent leaves, respectively.
4. The respiratory rate of mulberry leaves by night measured at 25°C was over 4mg CO₂ for young immature leaves, about 1mg CO₂ for mature ones and in the range of 0.5 to 1.0mg CO₂/100cm²/hr. for senescent ones.
5. It is supposed that the ability of stomate to close participated in the change with time in respiratory rate. Considering in connection with change in photosynthetic rate with the passage of time after the beginning of illumination, the decline in the ability of stomata to open and close may begin with the decline in the ability to close.