© 1994 Heron Publishing—Victoria, Canada
Diurnal patterns of leaf photosynthesis, conductance and water potential at the top of a lowland rain forest canopy in Cameroon:
measurements from the Radeau des Cimes
George W. Koch (1), Jeffrey S. Amthor (2) and Michael L. Goulden (3)
1. Department of Biological Sciences, Stanford University, Stanford, CA 94305-5020, USA / 2. Woods Hole Research Center, Woods Hole, MA 02543, USA / 3. Division of Applied Science and Department of Earth and Planetary Science, Harvard University, Cambridge, MA 02138, Canada / Received May 26, 1993
Summary
Diurnal patterns of leaf conductance, net photosynthesis and water potential of five tree species were measured at the top
of the canopy in a tropical lowland rain forest in southwestern Cameroon. Access to the 40 m canopy was by a large canopy-supported
raft, the Radeau des Cimes. The measurements were made under ambient conditions, but the raft altered the local energy balance at times, resulting in
elevated leaf temperatures. Leaf water potential was equal to or greater than the gravitational potential at 40 m in the early
morning, falling to values as low as –3.0 MPa near midday. Net photosynthesis and conductance were typically highest during
midmorning, with values of about 10–12 µmol CO2 m–2 s–1 and 0.2–0.3 mol H2O m–2 s–1, respectively. Leaf conductance and net photosynthesis commonly declined through midday with occasional recovery late in
the day. Photosynthesis was negatively related to leaf temperature above midday air temperature maxima. These patterns were
similar to those observed in other seasonally droughted evergreen communities, such as Mediterranean-climate shrubs, and indicate
that environmental factors may cause stomatal closure and limit photosynthesis in tropical rain forests during the midday
period.
Keywords:
leaf conductance, net photosynthesis, stomatal conductance, tropical rain forest.
