H. Eguchi

Dynamics of plant water relations as affected by evaporative demand

Abstract Evaporative demand was evaluated physically by using environmental factors of radiant flux density, air temperature, humidity and wind velocity. The evaluated evaporative demand explained quantitatively effects of the respective environmental factors on evaporation. Furthermore, a heat flux control method developed for on-line measurement of stem water flux was applicable to dynamic analysis of transpiration stream in a cucumber plant ( Cucumis sativus L.) responding to the evaporative demand. The evaporative demand and the stem base water flux closely related to stomatal response and leaf growth through dynamics of plant water balance. These facts suggest that plant water relations affected by environment can be better understood by online measurements of the evaporative demand and the transpiration stream.

Root temperature effect on hydraulic characteristics of roots in hydroponics

ABSTRACT Water uptake and gas exchange in cucumber roots ( Cucumis sativus L. cv Chojitsu-Ochiai) were examined in a root temperature control system of air-tightened hydroponics. The effect of root temperature on water uptake rate was found in a sigmoidal pattern: The water uptake rate was reduced at root temperatures lower than 12°C. The responses of O 2 decrease rate and CO 2 increase rate to the root temperatures appeared almost parallel to the pattern of water uptake rate. Furthermore, the effect of root temperature on total root resistance was examined in a detached root system by applying suction to the proximal end. The total root resistance became higher at lower root temperatures. Thus, it could be suggested that at the lower root temperatures, the increase in root hydraulic resistance in relation to the inhibited root respiration results in the decrease in water uptake in intact plants. On the other hand, the total root resistance at lower root temperatures in figleaf gourd plant ( Cucurbita ficifolia B.) which is more tolerant of low temperature were kept higher as compared with that of cucumber plant. This fact indicates that low temperature tolerance in plant growth closely relates to root hydraulic characteristics at the lower root temperatures.

Application of image processing to measurement of total length in root system

Newly developed method of image processing was applied to measurement of the total length in a root system. The image of cucumber root system was taken by a still video camera, and transformed into the thinned root image which was composed of the pixels. The counting operation of respective diagonal and horizontal or vertical connections of pixels was carried out, and the root length was calculated from the counted total numbers of the connections; a reliable correction factor was designed mathematically for diagonal connection. Estimation error was within 2% of actual length, and the correlation coefficient (r) between actual and estimated length was 0.9999 (P<0.01). Thus, the present method can be useful for simple and accurate measurement of root length and may help to understand the characteristics of plant root system.