The Relationship between Environmental Factors and Behaviour of Stomata in the Rice Plants : V. Effects of partial excision of root system on diurnal course of stomatal aperture

Abstract

The present investigation was undertaken to clarify the relationship between the behaviour of stomata and water absorption through thc roots in rice plants grown under submerged condition by measuring the diurnal course of stomatal aperture in rice plants with partially excised root system. No difference of stomatal aperture was found between plants with non-excised and partially excised root system in early morning when transpiration was not so remarkable and water content of leaf blades was still high (Fig. 2, 3). After about 11 a.m. on a fine day accompanied by intense transpiration, stomata closed to a more considerable extent in plants with partially excised root system than that of non-excised one, due to decrease of water content of leaf blades (Fig. 2, 3). The extent of stomatal closure is severer in lower leaves than in upper ones, especially in plants with partially excised root system, so that the difference of stomatal aperture between lower and upper leaves became larger in the afternoon (Fig. 4, Table 1). Leaf water content on an areal basis followed the diurnal variation pattern of taking the maximum value in early morning and decreasing towards atternoon. The decrease of leaf water content was rather remarkable in plants with partially excised root system than that of non-excised one on fine days, but the difference was smaller than was expected (Fig. 5). Leaf water saturation deficit was different significantly between plants with non-excised and partially excised root system in the afternoon on the fine day at the ripening stage (Table 2). From these results and the close relationship between stomatal aperture and photosynthetic rate, it is suggested that the decrease of water absorption in rice plants grown under submerged condition has much caring on the efficiency of light utilization in photosynthesis because of the stomatal closure in the afternoon on a fine day, in the same manner as the effect of water deficit in the soil.