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Title: Evaluating the potential of a novel dual heat-pulse sensor to measure volumetric water use in grapevines under a range of flow conditions

Author
item PEARSALL, KYLE - University Of California
item WILLIAMS, LARRY - University Of California
item BLEBY, TIM - University Of Western Australia
item CASTORANI, SEAN - University Of California
item McElrone, Andrew

Submitted to: Functional Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2014
Publication Date: 4/22/2014
Publication URL: http://www.publish.csiro.au/?act=view_file&file_id=FP13156.pdf
Citation: Pearsall, K., Williams, L., Bleby, T., Castorani, S., Mcelrone, A.J. 2014. Evaluating the potential of a novel dual heat-pulse sensor to measure volumetric water use in grapevines under a range of flow conditions. Functional Plant Biology. 41:874-883.

Interpretive Summary: In this manuscript, we describe the results of our efforts to develop and validate a new sap flow measurement technique for quantifying water use in grapevines under high, low and reverse flow conditions commonly seen in California vineyards. We combined two existing heat pulse sap flow techniques into a single sensor configuration and tested them against water use measurements obtained by a weighing lysimeter and with existing plant water use models. The new method effectively tracked the full range of sap velocities, but high variability between sensors within and across sensors made absolute volumetric estimates problematic. We feel the new sensor configuration is an effective research tool, but at this stage has limited applicability to real time irrigation needs.

Technical Abstract: The aim of this study was to validate dual sap flow sensors that combine two heat pulse techniques to measure volumetric water use over the full range of sap flows found in grapevines. The heat ratio method (HRM), which works well at measuring low and reverse flows, was combined with the compensation heat pulse method (CHPM) that captures moderate to high flows. Sap flow measurements were performed on mature Vitis vinifera L. (cvs. Thompson Seedless, Chardonnay, and Cabernet Sauvignon) grapevines growing in a field weighing lysimeter and vineyards in Fresno, Davis, and Oakville, CA. The combined heat pulse techniques closely tracked diurnal grapevine water use determined through lysimetry in two growing seasons, and this was true even at very high flow rates (> 6 L vine-1 h-1 for Thompson seedless vines in the weighing lysimeter ), where measurement errors have the greatest effect on daily cumulative water use estimates. Volumetric water use determined with heat pulse techniques was highly correlated to hourly lysimeter water use in both years (R2 = 0.92 and 0.95 in 2008 and 2009, respectively), but the nature of the relationship was inconsistent among replicate sensors. Similar results were obtained when comparing grapevine water use determined from sap flow sensors to miniaturized weighing lysimetry of two year-old potted vines grown in a greenhouse and to meteorological estimates for field-grown vines in Davis and Oakville. The inconsistency in the regression coefficients obtained from each of these data sets was likely due to variation in active sapwood around the grapevine trunks, which can be exacerbated by trunk diseases common to mature vineyards in this growing region. However, the robust nature of all of the correlations demonstrates that heat pulse techniques can be used to effectively track relative changes in grapevine water use.