title: Regulation of water flux through trunks, branches, and leaves in trees of a lowland tropical forest.
abstract: We studied regulation of whole-tree water use in individuals of five diverse canopy tree species growing in a Panamanian seasonal forest. A construction crane equipped with a gondola was used to access the upper crowns and points along the branches and trunks of the study trees for making concurrent measurements of sap flow at the whole-tree and branch levels, and vapor phase conductances and water status at the leaf level. These measurements were integrated to assess physiological regulation of water use from the whole-tree to the single-leaf scale. Whole-tree water use ranged from 379 kg day-1in a 35 m-tall Anacardium excelsum tree to 46 kg day-1in an 18 m-tall Cecropia longipes tree. The dependence of whole-tree and branch sap velocity and sap flow on sapwood area was essentially identical in the five trees studied. However, large differences in transpiration per unit leaf area (E) among individuals and among branches on the same individual were observed. These differences were substantially reduced when E was normalized by the corresponding branch leaf area:sapwood area ratio (LA/SA). Variation in stomatal conductance (gs) and crown conductance (gc), a total vapor phase conductance that includes stomatal and boundary layer components, was closely associated with variation in the leaf area-specific total hydraulic conductance of the soil/leaf pathway (Gt). Vapor phase conductance in all five trees responded similarly to variation in Gt. Large diurnal variations in Gtwere associated with diurnal variation in exchange of water between the transpiration stream and internal stem storage compartments. Differences in stomatal regulation of transpiration on a leaf area basis appeared to be governed largely by tree size and hydraulic architectural features rather than physiological differences in the responsiveness of stomata. We suggest that reliance on measurements gathered at a single scale or inadequate range of scale may result in misleading conclusions concerning physiological differences in regulation of transpiration.
authors.affiliation: Hawaii Agriculture Research Center, 99-193 Aiea Heights Drive, Aiea, Hawaii 96701, USA Fax: (808) 486-5020; e-mail: meinzer@hawaii.edu, , , , , , US.
authors.forename: José Luis
authors.initials: JL
authors.lastname: Andrade
authors.affiliation: Hawaii Agriculture Research Center, 99-193 Aiea Heights Drive, Aiea, Hawaii 96701, USA Fax: (808) 486-5020; e-mail: meinzer@hawaii.edu, , , , , , US.
authors.forename: Frederick C
authors.initials: FC
authors.lastname: Meinzer
authors.affiliation: Department of Botany, University of Hawaii, 3190 Maile Way, Honolulu, Hawaii 96822, USA, , , , , , US.
authors.forename: Guillermo
authors.initials: G
authors.lastname: Goldstein
authors.affiliation: Biological Laboratories, Harvard University, Cambridge, MA 02138, USA, , , , , , US.
authors.forename: N Michele
authors.initials: NM
authors.lastname: Holbrook
authors.affiliation: Departamento de Ciencias Biológicas, Universidad de los Andes, Bogotá, Colombia, , , , , , CO.
authors.forename: Jaime
authors.initials: J
authors.lastname: Cavelier
authors.affiliation: Department of Biology, University of California, Los Angeles, CA 90024, USA, , , , , , US.
authors.forename: Paula
authors.initials: P
authors.lastname: Jackson
authors.affiliation: Smithsonian Tropical Research Institute, Apartado 2072, Balboa, Republic of Panama, , , , , , PA.
authors.forename: Katia
authors.initials: K
authors.lastname: Silvera
keywords: Key words Hydraulic conductance; Sap flow; Stomata; Transpiration; Tropical forest trees