Submitted to: International Workshop on Sap Flow
Publication Type: Abstract Only
Publication Acceptance Date: April 25, 2008
Publication Date: October 21, 2008
Citation: Tarara, J.M. Estimating high rates of transpiration in woody vines with the heat-balance method. International Workshop on Sap Flow. Conference booklet. p.84. Technical Abstract: Heat-balance sap flow gauges were configured to produce a more thermally uniform stem cross section under high flow rates. On mature grapevines (Vitis labruscana) either undisturbed in the field or transplanted to large containers (ca. 1m3 volume), with stem diameters up to 46 mm and leaf area per vine up to 27 m2, custom-built gauges under variable power were run simultaneously with a whole-plant gas exchange system and a large balance (container vines only). Transpiration varied from about 80 g h-1 overnight to daily maxima approaching 2100 g h-1 (container vines) and 2700 g h-1 (field vines). In container vines, instantaneous estimates of transpiration (6.00 to 20.00 LST) agreed most closely between gas exchange and gravimetry ([Spearman Rank] R = 0.96; p<0.05). Estimates of transpiration were correlated significantly (p<0.05) between sap flow and gas exchange (R = 0.94), and between sap flow and gravimetry (R = 0.88). On average, cumulative estimates of transpiration over 24 h (17 to 19 L d-1) agreed within 5% (gravimetry vs. gas exchange) and within 17% (sap gauge vs. gas exchange or gravimetry). In field vines, instantaneous estimates of transpiration were correlated significantly (p<0.05) between sap flow and gas exchange (R = 0.87). Cumulative water use per vine was 18 to 22 L d-1; estimation methods differed on average by 15%. In both container and field vines, sap flow gauges appeared to underestimate high mid-day rates of transpiration consistently, due in part to the choice of power input. The open-loop power control algorithm maintained upstream-downstream surface temperature differences (dT) between 1.5 and 2 C during midday.