© 1996 Heron Publishing—Victoria, Canada
Diurnal changes in leaf gas exchange characteristics in the uppermost canopy of a rain forest tree, Dryobalanops aromatica Gaertn. f.
Atsushi Ishida (1), Takeshi Toma (1), Yoosuke Matsumoto (1), Son Kheong Yap (2) and Yutaka Maruyama (3)
1. Forest Environment Division, Forestry and Forest Products Research Institute, P.O. Box 16, Tsukuba Norin Danchi, Ibaraki 305,
Japan / 2. Forest Research Institute of Malaysia, Kepong 52109, Kuala Lumpur, Malaysia / 3. Japan International Research Center for Agricultural Science, Tsukuba, Ibaraki 305, Japan / Received October 13, 1995
Summary
Dryobalanops aromatica Gaertn. f. is a major tropical canopy species in lowland tropical rain forests in Peninsular Malaysia. Diurnal changes in
net photosynthetic rate (A) and stomatal conductance to water vapor (gs) were measured in fully expanded young and old leaves in the uppermost canopy (35 m above ground). Maximum A was 12 and 10 µmol m–2 s–1 in young and old leaves, respectively; however, because of large variation in A among leaves, mean maximum A in young and old leaves was only 6.6 and 5.5 µmol m–2 s–1, respectively. Both gs and A declined in young leaves when Tleaf exceeded 34 °C and leaf-to-air vapor pressure deficit (ΔW) exceeded 0.025, whereas in old leaves, gs and A did not start to decline until Tleaf and ΔW exceeded 36 °C and 0.035, respectively. Under saturating light conditions, A was linearly related to gs. The coefficient of variation (CV) for the difference between the CO2 concentrations of ambient air and the leaf intercellular air space (Ca – Ci) was smaller than the CV for A or gs, suggesting that maximum gs was mainly controlled by mesophyll assimilation (A/Ci). Minimum Ci/Ca ratios were relatively high (0.72–0.73), indicating a small drought-induced stomatal limitation to A and non-conservative water use in the uppermost canopy leaves.
Keywords:
drought, irradiance, photosynthesis, stomatal conductance, tropical rain forest, uppermost canopy, water deficit.
