Diurnal and phenological changes of bleeding rate in lowland rice plants

Abstract

The bleeding rate of rice plants grown in the farmer's paddy field was examined for use as an index of root activity. The bleeding rate started to decrease immediately after removing the shoot of rice plants. Therefore, the diurnal change of bleeding rate was examined using new different individuals for each measurement. The bleeding rate increased to reach the maximum value in the morning and decreased thereafter. On the other hand, the maximum bleeding rate of the day increased gradually to reach the maximum around the heading stage, and thereafter decreased rapidly. Next, the bleeding rate was divided by the accumulated leaf number, which is known to be closely related to the total root number, to evaluate the bleeding rate per unit root number. The bleeding rate per leaf number started to decrease gradually at the early develomental stage and decreased rapidly after the heading. Because new roots emerge successively, the bleeding rate of the whole plant increased gradually, even though bleeding rate per unit root number decreased. The bleeding rate decreased rapidly after the heading, because new roots did not emerge after heading and senescence of the roots proceeded.