title: Influence of stem temperature changes on heat pulse sap flux density measurements.
abstract: While natural spatial temperature gradients between measurement needles have been thoroughly investigated for continuous heat-based sap flow methods, little attention has been given to how natural changes in stem temperature impact heat pulse-based methods through temporal rather than spatial effects. By modelling the theoretical equation for both an ideal instantaneous pulse and a step pulse and applying a finite element model which included actual needle dimensions and wound effects, the influence of a varying stem temperature on heat pulse-based methods was investigated. It was shown that the heat ratio (HR) method was influenced, while for the compensation heat pulse and Tmax methods changes in stem temperatures of up to 0.002 °C s(-1) did not lead to significantly different results. For the HR method, rising stem temperatures during measurements led to lower heat pulse velocity values, while decreasing stem temperatures led to both higher and lower heat pulse velocities, and to imaginary results for high flows. These errors of up to 40% can easily be prevented by including a temperature correction in the data analysis procedure, calculating the slope of the natural temperature change based on the measured temperatures before application of the heat pulse. Results of a greenhouse and outdoor experiment on Pinus pinea L. show the influence of this correction on low and average sap flux densities.
authors.affiliation: Laboratory of Plant Ecology, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, 9000 Gent, Belgium maurits.vandegehuchte@ugent.be.
authors.forename: Maurits W
authors.initials: MW
authors.lastname: Vandegehuchte
authors.affiliation: School of Plant Biology, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia.
authors.forename: Stephen S O
authors.initials: SS
authors.lastname: Burgess
authors.affiliation: School of Plant Biology, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia ICT International, 211 Mann St, Armidale, NSW 2350, Australia.
authors.forename: Alec
authors.initials: A
authors.lastname: Downey
authors.affiliation: Laboratory of Plant Ecology, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, 9000 Gent, Belgium.
authors.forename: Kathy
authors.initials: K
authors.lastname: Steppe
mesh_terms: D006358:Hot Temperature; D008954:Models, Biological; D028223:Pinus / Q000502:physiology*; D053147:Plant Exudates; D018547:Plant Stems; D018526:Plant Transpiration; D012107:Research Design; D013696:Temperature; D014197:Trees / Q000502:physiology*; D014867:Water / Q000502:physiology*; D052584:Xylem / Q000502:physiology*
chemical_list: D053147:Plant Exudates; D014867:Water
keywords: heat dissipation; sap flow; sensor; transpiration