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Am. J. Enol. Vitic. 52:3:260-265 (2001)
Copyright © 2001 by the American Society for Enology and Viticulture.
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Device for Simulating High Rates of Sap Flow in Grapevines

J.M. Tarara 1 and J.C. Ferguson 1

1 USDA-ARS, Horticultural Crops Research Unit, 24106 N. Bunn Rd., Prosser, WA 99350.

jtarara{at}tricity.wsu.edu

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.

Key words: Vitis, heat-balance method, sap gauge, water use, transpiration, measurement, stem flow, woody species, methodology




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Copyright © 2001 by the American Society for Enology and Viticulture.