Applicability of thermal dissipation probe in the determination of trunk flow of Platycladus orientalis under cyclic heating mode

Abstract

To evaluate the adaptability of the cyclic heating mode in the thermal diffusion probe method (TDP) in the measurement of trunk sap flow and the accuracy of the measurement of tree transpiration water consumption, we selected Platycladus orientalis as the research object and set three different heating modes: 60 min/0 min (continuous heating mode), 30 min/30 min (cyclic heating mode with 30 min heating and 30 min cooling), 10 min/50 min (cyclic heating mode with 10 min heating and 50 min cooling). Based on the measured value of the whole tree container wei-ghing method, the temperature gradient characteristics of different heating modes were analyzed using the measurement technology of thermal diffusive trunk sap flow. The Granier's corrected formulas of cyclic heating modes were constructed, with its error being analyzed by validity verification. The results showed that sap flow rate calculated by the cyclic heating mode was consistent with the diurnal variation of the transpiration rate measured by the whole tree weighing method. The temperature of cyclic heating mode could quickly rise, fall and performed stably. The sap flow calculated by Granier's original formula was 61.3% lower than that by weighing method. The corrected Granier formula in the mode of 10 min/50 min and 30 min/30 min were Fd=0.0177K0.9457 (R2=0.88) and Fd=0.0378K1.3146(R2=0.85), respectively. The difference of sap flow rate in P. orientalis by the new formula was smaller than that measured by the whole tree weighing method, and the error of transpiration rate calculated by the 10 min/50 min correction formula was the smallest, 5.9% lower than that calculated by the weighing method, and thus could express the real flow rate. The 10 min/50 min cyclic heating mode could be used to reduce the effect of natural temperature difference, cut down power consumption, and accurately reflect the actual sap flow rate of P. orientalis.