Sap flow changes in‘Kuerle Xiangli'trees with three different canopy shapes and their relationships with climatic factors

【Objective】The sap flow in‘Kuerle Xiangli'with three different canopy shapes was continuously monitored to unravel the characteristics of plant transpiration discuss the correlation between sap flow in trees with three different canopy shapes and climatic factors. Consequently, models of transpiration water-consumption were constructed so as to lay theoretical foundation for achieving the regional scale from single tree water-consumption to population water-consumption, for improving water use efficiency in pear trees, for developing orchard water-saving irrigation technology and for improving orchard ecosystem management.【Methods】A PS-TDP8 thermal dissipation probe sap flow measuring system was used to monitor sap flow in‘Kuerle Xiangli'trees with three shapes. The instrument was placed in a protective box which was located in middle positions of the three trees about 40 cm above ground. A drill bit of 2.0 mm in diameter was used to drill 22 mm deep holes in branches. Drill another hole 10 cm below the hole.Push the probe into one of holes to the set depth and push a reference probe into another hole. Each sen-sor had two probes, both of which had a heater, but the probe with a red mark was heated while the one with a green mark was unheated and served as the reference. Both probe heaters were coated evenly with a heat conductive grease before they were inserted gently into the holes to the set depth. The heated probe was at the upper position and the reference one at the lower position. After probe installation was completed, they were covered with a bubblewrap, which extended 30-40 cm above and below the probes. Then the whole wrapped part was covered with enforced aluminum foil to ensure a good heat/radiation insulation. At the top of the cover, the gap between the cover and the tree bark was sealed to prevent rainwater from coming in. Finally, the operating voltage for thermocouple detection of the thermal dissipation sap flow system was adjusted using CR1000 type data acquisition and PC400. The data logger had an automatic acquisition period of 10 seconds and data were stored every 30 minutes. A Davis weather station was installed in a representative area in the central pear the orchard, and three climatic parameters including light intensity(w · m- 2), air temperature(℃) and air relative humidity(%) were continuously monitored.【Results】The sap flow of‘Kuerle Xiangli'trees with different canopy shapes was high during daytime and low in the night. Sap flow changed significantly during daytime especially from 9 am to 12 am, and it reached a peak value around 2 pm. But after 9 pm, the sap flow became extremely weak, and basically stopped from 1 am to 8 am. The change trend of sap flow among the three canopy shapes was basically same, but there were also some discrepancies. The magnitude of sap flow and range of variation followed a descending order of evacuation shape> trellis shape> open center shape. The sap flow of the three tree shapes all began to rise around 8:30 am and reached a maximum around 3 pm. Then, it decreased rapidly around 5:30 pm. The mean and peak values of sap flow of the three tree shapes were different. The mean value of the trellis shape and the evacuation shape was 1.31 and 1.59 times that of the open center shape,respectively. The peak sap flow of the trellis shape and the evacuation shape was 1.38 and 1.44 times higher than that of the open center shape. The changes in sap flow flux were correlated with the changes in climatic parameters. The correlation coefficent between sap flow and climatic factors in the trellis shape followed the order of light intensity> air temperature > vapor pressure deficit > air relative humidity, which was as same in the case of the evacuation shape. While the correlation coefficient between sap flow and climatic parameter in the open center shape followed the order of vapor pressure deficit> light intensity>air temperature > air relative humidity. The changes in sap flow and the changes in climatic factors were not synchronized, and there was a time- delay phenomena. The changes in sap flow of the three tree shapes all lagged behind light intensity but earlier than air temperature and vapor pressure deficit. Ridge regression equations could be constructed between sap flow of different tree shapes and light intensity, air temperature and relative humidity. The variance analysis showed that these equations could well reveal the correlation between sap flow of each of the tree shapes of‘Kuerle Xiangli'trees and climatic parameters【.Conclusion】The sap flow in‘Kuerle Xiangli'trees of three canopy shapes changed due to the change of light intensity, air temperature and air relative humidity. As a result, sap flow showed significant fluctuation, being high during daytime and low during nighttime. The sap flow in trees with different canopy shapes was different, and that of the open center shape was the lowest and its variation range was the smallest. The changes in sap flow and the changes in climatic factors were not synchronized. The changes in sap flow of the three canopy shapes all lagged behind light intensity but earlier than the air temperature and vapor pressure deficit. Changes in sap flow were closely related to climatic factors. However, light intensity and air temperature were the most important factors.