title: Transpiration of a 64-year-old maritime pine stand in Portugal : 1. Seasonal course of water flux through maritime pine.
abstract: The transpiration, sap flow, stomatal conductance and water relations ofPinus pinaster were determined during spring and summer in a 64-year-old stand in Ribatejo (Portugal). The transpiration of the pine canopy was determined from sap flow or eddy covariance techniques. Canopy conductance values (gc) were estimated from inversion methods using eddy covariance or sap flow data, respectively, and from scaling-up methods using stomatal conductance values measured in the field and leaf area index (LAI) values. The transpiration was closely controlled by the stomatal conductance of pines (Ω was 0.05-0.15). For wet soil conditions, the various estimates ofgcshowed reasonable agreement.gcpeaked in the morning at 0.01 m×s-1, exhibited a midday depression and showed a secondary peak in late afternoon. This behaviour could be predicted simply on the basis of the stomatal sensitivity to air vapour pressure deficit. On a seasonal basis, monthly average values ofgcdecreased from 4×10-3m×s-1in spring to 1.7×10-3m·s-1in late summer. Accordingly, the transpiration peaked at 3 mm×d-1on wet soil in May. It decreased progressively during the summer drought to 0.8 mm×d-1at the end of August. The minimal value of needle water potential was maintained at -1.9 MPa but predawn values decreased from -0.6 MPa in May to -0.9 MPa in July. It may have reached lower values in August. The amount of water stored in the trunk accounted for a 12% (10 kg×tree-1×day-1) of the daily transpiration in spring. The storage capacity of the canopy was within the same order of magnitude. The trunk storage increased to 25% (13 kg×tree-1×day-1) of the daily transpiration at the end of summer under drought conditions. The sap flow beneath the crown lagged accordingly behind transpiration with a time constant estimated between 26 min in spring and 40 min at the end of summer.
authors.affiliation: Station de Recherches Forestières, INRA Centre de Bordeaux, BP45, F-33611, Gazinet, France.
authors.forename: D
authors.initials: D
authors.lastname: Loustau
authors.affiliation: Station de Bioclimatologie, INRA Centre de Bordeaux, BP 81, F-33883, Villenave d'Ornon, France.
authors.forename: P
authors.initials: P
authors.lastname: Berbigier
authors.affiliation: Station de Recherches Forestières, INRA Centre de Bordeaux, BP45, F-33611, Gazinet, France.
authors.forename: P
authors.initials: P
authors.lastname: Roumagnac
authors.affiliation: Instituto Superior de Agronomia, Technical University of Lisbon, Tapada da Ajuda, 1399, Lisboa codex, Portugal.
authors.forename: C
authors.initials: C
authors.lastname: Arruda-Pacheco
authors.affiliation: Instituto Superior de Agronomia, Technical University of Lisbon, Tapada da Ajuda, 1399, Lisboa codex, Portugal.
authors.forename: J S
authors.initials: JS
authors.lastname: David
authors.affiliation: Instituto Superior de Agronomia, Technical University of Lisbon, Tapada da Ajuda, 1399, Lisboa codex, Portugal.
authors.forename: M I
authors.initials: MI
authors.lastname: Ferreira
authors.affiliation: Instituto Superior de Agronomia, Technical University of Lisbon, Tapada da Ajuda, 1399, Lisboa codex, Portugal.
authors.forename: J S
authors.initials: JS
authors.lastname: Pereira
authors.affiliation: Instituto Superior de Agronomia, Technical University of Lisbon, Tapada da Ajuda, 1399, Lisboa codex, Portugal.
authors.forename: R
authors.initials: R
authors.lastname: Tavares
keywords: Pinus pinaster Ait; Sap flux; Stomatal conductance; Transpiration; Water storage