On the Diurnal Variation of Leaf Water Content on an Areal Basis in the Rice Plant

[摘要] In a previous report4) it was made clear that the stomata of leaf blade of rice plants closed to a considerable extent on fine days even when they grew in submerged paddy field. For this time an investigation was undertaken to clarify the diurnal variation of leaf water content on an areal basis in some developmental stages of rice plants under various weather conditions. Maximal water content was obtained for 12th and 13th leaf, fully expanded just at the panicle formation stage. The water content decreased more and more for both upper and lower leaves as away from the relevant leaves. The water content of each successive leaf followed the diurnal variation pattern of taking the maximal value in eariy morning and decreasing towards noon. But the range of variation was wider at the tillering stage, becoming narrower after the booting stage. As for the effect of weather condition, the midday decrease of water content was rather remarkable on fine days accompanied with intense transpiration, but the difference of diurnal variation between fine and cloudy days was small as was expected. From this result it was suggested that the water content of rice plants grown in submerged condition did not debrease below a certain limit, owing perhaps to the increase of water absorption in accordance with intensive transpiration or stomatal closure due to the decrease of water content. In the afternoon of fine days, stomatal aperture became much smaller than on cloudy days. So it was considered that the slight variation of water content gave much influence upon stomatal aperture when water content of leaf blade decreased to a certain limit and that this influcnce became more prominent after the booting stage with narrower range of the variation of water content. Lastly the areal weight or the dry weight per leaf area was much larger in fine days compared with cloudy days, suggesting the effect of dry weight increase upon the decrease of customary leaf water content on a dry weight or fresh weight basis.

[学科分类] 农业科学（综合）