© 2005 Heron Publishing—Victoria, Canada
Stomatal conductance, transpiration and sap flow of tropical montane rain forest trees in the southern Ecuadorian Andes
Thomas Motzer (1, 2, 3), Nicole Munz (1), Manfred Küppers (4), Dieter Schmitt (4) and Dieter Anhuf (5)
1. University of Mannheim, Department of Physical Geography, L9, 1–2, D-68131 Mannheim, Germany / 2. Corresponding author (thomas.motzer@web.de) / 3. Eichendorffstrasse 33, 68167 Mannheim, Germany / 4. University of Hohenheim, Institute of Botany and Botanical Garden, Garbenstr. 30, D-70599 Stuttgart, Germany / 5. Department of Physical Geography, University of Passau, Innstr. 40, D-94032 Passau, Germany / Received October 18, 2004; accepted March 5, 2005; published online August 1, 2005
Summary
We investigated tree water relations in a lower tropical montane rain forest at 1950–1975 m a.s.l. in southern Ecuador. During
two field campaigns, sap flow measurements (Granier-type) were carried out on 16 trees (14 species) differing in size and
position within the forest stand. Stomatal conductance (gs) and leaf transpiration (El) were measured on five canopy trees and 10 understory plants. Atmospheric coupling of stomatal transpiration was good (decoupling
coefficient Ω = 0.25–0.43), but the response of gs and El to the atmospheric environment appeared to be weak as a result of the offsetting effects of vapor pressure deficit (VPD)
and photosynthetic photon flux (PPF) on gs. In contrast, sap flow (F) followed these atmospheric parameters more precisely. Daily F depended chiefly on PPF sums, whereas on short time scales, VPD impeded transpiration when it exceeded a value of 1–1.2 kPa.
This indicates an upper limit to transpiration in the investigated trees, even when soil water supply was not limiting. Mean
gs was 165 mmol m–2 s–1 for the canopy trees and about 90 mmol m–2 s–1 for the understory species, but leaf-to-leaf as well as tree-to-tree variation was large. Considering whole-plant water use,
variation in the daily course of F was more pronounced among trees differing in size and crown status than among species. Daily F increased sharply with stem diameter and tree height, and ranged between 80 and 120 kg day–1 for dominant canopy trees, but was typically well below 10 kg day–1 for intermediate and suppressed trees of the forest interior.
Keywords:
atmospheric coupling of transpiration, stomatal control, tree water relations, tropical mountain.
