Abstract
Sap-flow gauges typically are tested by comparing their output to gravimetric measurements of water loss from a potted plant. However, a mature vine of Vitis labrusca cv. Concord, when potted, could not achieve the high rates of sap flow that were observed in similar vines in the field. This limited the range in which the sap-flow gauges could be tested and confidence in their accuracy at high flow rates. Consequently, a laboratory device was constructed to reproduce the high rates of sap flow that were observed in the vineyard on mature grapevines. The device allows gauge testing on a severed vine stem, thereby reproducing the thermal regime of a sap-flow measurement in the field. The design of the device is simple, and its component parts are low cost and easily obtained from commercial sources. The device permits empirical determination of limiting factors in gauge performance as they vary with flow rate. It also permits the establishment of "zero-flow set" or gauge conductance on hydrated stem tissue. Evaluation of the heat-balance method under high rates of sap flow (>1500 g h-1) showed that gauges made from designs that are standard in the literature consistently underestimated gravimetric measurements. Evidence suggests that gauges should be redesigned to accommodate thermal heterogeneity across the vine stem that occurs under high flow.
- Vitis
- heat-balance method
- sap gauge
- water use
- transpiration
- measurement
- stem flow
- woody species
- methodology
- Copyright 2001 by the American Society for Enology and Viticulture
Sign in for ASEV members
ASEV Members, please sign in at ASEV to access the journal online.
Sign in for Institutional and Non-member Subscribers
Log in using your username and password
Pay Per Article - You may access this article (from the computer you are currently using) for 2 day for US$10.00
Regain Access - You can regain access to a recent Pay per Article purchase if your access period has not yet expired.