© 2004 Heron Publishing—Victoria, Canada
Dynamics of transpiration, sap flow and use of stored water in tropical forest canopy trees
Frederick C. Meinzer (1, 2), Shelley A. James (3) and Guillermo Goldstein (4)
1. USDA Forest Service, Forestry Sciences Laboratory, 3200 SW Jefferson Way, Corvallis, OR 97331, USA / 2. Corresponding author (fmeinzer@fs.fed.us) / 3. Pacific Center for Molecular Biodiversity, Bishop Museum, Honolulu, HI 96817, USA / 4. Department of Biology, University of Miami, Coral Gables, FL 33124, USA / Received October 23, 2003; accepted February 15, 2004; published online June 1, 2004
Summary
In large trees, the daily onset of transpiration causes water to be withdrawn from internal storage compartments, resulting
in lags between changes in transpiration and sap flow at the base of the tree. We measured time courses of sap flow, hydraulic
resistance, plant water potential and stomatal resistance in co-occurring tropical forest canopy trees with trunk diameters
ranging from 0.34–0.98 m, to determine how total daily water use and daily reliance on stored water scaled with size. We also
examined the effects of scale and tree hydraulic properties on apparent time constants for changes in transpiration and water
flow in response to fluctuating environmental variables. Time constants for water movement were estimated from whole-tree
hydraulic resistance (R) and capacitance (C) using an electric circuit analogy, and from rates of change in water movement through intact trees. Total daily water use
and reliance on stored water were strongly correlated with trunk diameter, independent of species. Although total daily withdrawal
of water from internal storage increased with tree size, its relative contribution to the daily water budget (~10%) remained
constant. Net withdrawal of water from storage ceased when upper branch water potential corresponded to the sapwood water
potential (Ψsw) at which further withdrawal of water from sapwood would have caused Ψsw to decline precipitously. Stomatal coordination of vapor and liquid phase resistances played a key role in limiting stored
water use to a nearly constant fraction of total daily water use. Time constants for changes in transpiration, estimated as
the product of whole- tree R and C, were similar among individuals (~0.53 h), indicating that R and C co-varied with tree size in an inverse manner. Similarly, time constants estimated from rates of change in crown and basal
sap flux were nearly identical among individuals and therefore independent of tree size and species.
Keywords:
allometric relationships, hydraulic architecture, hydraulic capacitance, hydraulic resistance, scaling, time constants.
