Use of gravimetric measurements to calibrate thermal dissipation probes with stem segments

Abstract

AbstractTree transpiration is an important part of the global water cycle, and it is frequently represented by sap flow measurements at the individual plant scale. The thermal dissipation probes (TDPs) are commonly employed to measure and calculate sap flows, for which Granier equation is generally used. However, the original Granier equation has been found to underestimate sap flow rates. Calibration methods using different materials (i.e., whole trees or stem segments) have been proposed to recalibrate TDPs; however, these methods are often either expensive or complicated. This study proposes a new device that uses the gravimetric measurement method (GMM) to recalibrate TDPs. The GMM is relatively simple and easy to conduct. The proposed device uses a tube and siphon to maintain a constant pressure; an electronic balance is used to measure the actual sap flow. Four plant species with different stem porosity types, Pyrus pyrifolia (diffuse‐porous), Quercus fabri (ring‐porous), Platycarya strobilacea (ring‐porous) and Kalopanax septemlobus (ring‐porous), were selected to examine the performance of the GMM. The results showed that: (1) good correlations were obtained between the actual sap flow (from gravimetric measurements) and sap flow estimates obtained using the original TDP technique; (2) the results of the GMM‐recalibrated TDP measurement equation greatly differed from those of the original Granier calibration equation; and (3) the recalibration equation derived from the GMM outperformed the original Granier equation. This study suggests that the developed GMM can be used to recalibrate TDPs, and that using this method can help to improve sap flow measurements, thereby improving estimates of tree water consumption and transpiration.