title: Radial profiles of sap flow with increasing tree size in maritime pine.
abstract: We investigated the radial variation of sap flow within sapwood below the live crown in relation to tree size in 10-, 32-, 54- and 91-year-old maritime pine stands (Pinus pinaster Ait.). Radial variations were determined with two thermal dissipation sensors; one measured sap flux in the outer 20 mm of the xylem (Jref), whereas the other was moved radially across the sapwood in 20-mm increments to measure sap flux at multiple depths (Jref). For all tree sizes, sap flow ratios (Ri = JiJref (-1)) declined with increasing sapwood depth, but the decrease was steeper in trees with large diameters. Correction factors (C) were calculated to extrapolate Jref for an estimate of whole-tree sap flux. A negative linear relationship was established between stem diameter and C, the latter ranging from 0.6 to 1.0. We found that neglecting these radial corrections in 10-, 32-, 54- and 91-year-old trees would lead to overestimation of stand transpiration by 4, 14, 26 and 47%, respectively. Therefore, it is necessary to account for the differential radial profiles of sap flow in relation to tree size when comparing tree transpiration and hydraulic properties among trees differing in size.
authors.affiliation: Unité-EPHYSE, INRA, 69 route d'Arcachon, 33612 GAZINET Cedex, France. delzon@pierroton.inra.fr
authors.forename: Sylvain
authors.initials: S
authors.lastname: Delzon
authors.forename: Michel
authors.initials: M
authors.lastname: Sartore
authors.forename: André
authors.initials: A
authors.lastname: Granier
authors.forename: Denis
authors.initials: D
authors.lastname: Loustau
mesh_terms: D028223:Pinus / Q000502:physiology*; D018547:Plant Stems / Q000502:physiology; D018526:Plant Transpiration / Q000502:physiology; D014197:Trees / Q000502:physiology*; D014867:Water / Q000378:metabolism
chemical_list: D014867:Water