| Abstract: | Transient responses of sap flow to step changes in wind speedwere experimentally investigated in a wind tunnel. A Granier-typesap flow sensor was calibrated and tested in a cylindrical tubefor analysis of its transient time response. Then the sensorwas used to measure the transient response of a well-wateredPachira macrocarpa plant to wind speed variations. The transientresponse of sap flow was described using the resistance–capacitancemodel. The steady sap flow rate increased as the wind speedincreased at low wind speeds. Once the wind speed exceeded 8.0m s–1, the steady sap flow rate did not increase further.The transpiration rate, measured gravimetrically, showed a similartrend. The response of nocturnal sap flow to wind speed variationwas also measured and compared with the results in the daytime.Under the same wind speed, the steady sap flow rate was smallerthan that in the daytime, indicating differences between diurnaland nocturnal hydraulic function, and incomplete stomatal closureat night. In addition, it was found that the temporal responseof the Granier sensor is fast enough to resolve the transientbehaviour of water flux in plant tissue. Key words: Nocturnal transpiration, sap flow, transient response, wind speed
Received 31 July 2008; Revised 6 October 2008 Accepted 20 October 2008 |
