Assessment of the effect of water deficit on sap flow of longkong trees by using heat-pulse method

The effect of water deficit on sap flow of longkong trees was studied by using heat-pulse method. An experiment was carried out in a glasshouse over 30-day period. There were 3 treatments: 1) daily watering or control, 2) 5-day interval watering or moderate water deficit (MWD) and 3) 10-day interval watering or high water deficit (HWD) with 4 replications. Twelve longkong trees (3-year old) were used. Each tree was grown in a 30L polybag filled with soil mixture. It was found that leaf water potential, stomatal conductance and Fv/Fm (at 10 day interval) in the MWD and HWD continuously decreased through the experimental period, and they were significantly different from those of the control at the end of the experimental period. Sap flow in the MWD and HWD treatments were consistently low around day 16 and day 13 after starting the experiment. Concomitantly, stomatal conductance of HWD rapidly decreased from day 10, and it was significantly different from those in MWD and control treatments. This implies that water deficit caused stomatal closure leading to the reduction of transpiration. Hence, it appears that water deficit causes the decrease of sap flow in longkong tree, and this incidence depends on the severity of water deficit

Development a heat-pulse sapflow sensor to continuously record water use in fruit trees

The prototype of a heat-pulse sapflow sensor (PSU-TTSF) was developed for continuous recording of sapflow. The efficiency of the measurement of PSU-TTSF was evaluated by comparing with the Greenspan Sapflow Sensor (a commercial equipment). The 10-year old longkong trees were used as the test plants. The results showed that both equipments could be used for continuously automated records. The accuracy of the measurement was evaluated, and it was found that the sap flow values measured by PSU-TTSF exhibited high relationship with those values measured by Greenspan Sapflow Sensors. The sap flow measured by PSUTTSF tended to be lower, and the difference was approximately 16%. To reduce the error of measurement, the method of installing PSU-TTSF probe set needs to be improved by using a drill guide