Heat pulse 法によるセイヨウナシの枝, 果柄並びに葉柄内の水移動速度の測定

Abstract

It is important to investigate water transport through fruit trees because fruit production concerns greatly to water relationships in several aspects. In the present study, water transports in stems, peduncles and petioles in pear trees were investigated by a heat pulse method. The results may be summarized as follows:1. The heat pulse velocities and the actual flow rates (sap velocities) in pear trees were obtained by Closs′ analysis. Further, the sap velocities and its possible shifts of the directions in the peduncles and the petioles were measured directly by a application of the analysis.2. Heat pulse velocities were tested to detect the optimum depths of the installations in several pear stems using small thermal sensors (thermocouples of differential type) and heaters. Further, the effects of times of heat pulsing, voltages of source of electricity to the heaters and distance ratios of the 2 sensors (x:x') on the heatpulse velocities were measured in pear shoots. And measuring cautions were obtained in adapting the method for pear trees.3. The heat pulse velocities in shoots were in proportion to numbers of attached leaves. And the sap velocities related to several factors concerning transpiration rate and transpiration demand. Especially it related greatly to the degrees of the slope of water potentials between the xylems in the shoot base and the mesophyll. The water potentials of the latter fell down as the result of the leaf transpiration. Different diurnal changes in the sap velocities were found among 4 directions in the canopy. The sap velocities in the shoots at the inner canopy were lower than that at the outer canopy (the latter was about 1.6 times as high as the former on the average of the all directions in the daytime). The inclinations of the shoots did not affect on the heat pulse velocities at the outer canopy. But since the almost horizontal and inclined shoots had fewer leaves than the upward ones and existed at the inner canopy, it seemed that these shoots would have lower velocities than the upward ones at the outer canopy.4. Diurnal changes in water potentials in leaves, fruits and stems of Bartlett pear trees were measured. Further, diurnal changes in the sap velocities and the directions in peduncles and petioles of Bartlett pear trees were measured using the very tiny sensors. The reverse water transports from the fruits in the daytime were found and its typical velocities (about 0.8ml peduncle-1h-1 at maximum rate) were measured directly. These results coincided to the judgemental results from the authors′ model (“branched and confluent pipe stream model”) in the phenomena of competition of water between the fruits and the leaves. The pattern of watertranports between the two shifted in the fixed order, namely, the confluent stream to fruits in the nighttime→the branched stream in the early morning→the confluent stream to leaves in the daytime→the branched stream in the evening.