JXB Advance Access originally published online on November 20, 2008
Journal of Experimental Botany 2009 60(1):249-255; doi:10.1093/jxb/ern282
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© 2008 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
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RESEARCH PAPER |
Transient response of sap flow to wind speed
1Department of Civil Engineering, National Central University, Taiwan
2Department of Bioenvironmental Systems Engineering, National Taiwan University, Taiwan
3Department of Geography and Environment, Boston University, Boston, MA, USA
* To whom correspondence should be addressed. E-mail: crchu{at}cc.ncu.edu.tw
Transient responses of sap flow to step changes in wind speed were experimentally investigated in a wind tunnel. A Granier-type sap flow sensor was calibrated and tested in a cylindrical tube for analysis of its transient time response. Then the sensor was used to measure the transient response of a well-watered Pachira macrocarpa plant to wind speed variations. The transient response of sap flow was described using the resistance–capacitance model. The steady sap flow rate increased as the wind speed increased at low wind speeds. Once the wind speed exceeded 8.0 m s–1, the steady sap flow rate did not increase further. The transpiration rate, measured gravimetrically, showed a similar trend. The response of nocturnal sap flow to wind speed variation was also measured and compared with the results in the daytime. Under the same wind speed, the steady sap flow rate was smaller than that in the daytime, indicating differences between diurnal and nocturnal hydraulic function, and incomplete stomatal closure at night. In addition, it was found that the temporal response of the Granier sensor is fast enough to resolve the transient behaviour 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