© 2001 Heron Publishing—Victoria, Canada
Is elevation of carbon dioxide concentration beneficial to seedling photosynthesis in the understory of tropical rain forests?
Naishen Liang (1), Y. Tang (2) and T. Okuda (2)
1. Center for Global Environmental Research, National Institute for Environmental Studies, Onogawa 16-2, Tsukuba, Ibaraki 305-8506,
Japan / 2. Global Environment Division, National Institute for Environmental Studies, Onogawa 16-2, Tsukuba, Ibaraki 305-8506, Japan / Received June 1, 2000
Summary
Cuttings of the southeast Asian tropical rain forest tree species, Pongamia pinnata (L.) Pierre were raised in growth chambers providing a photosynthetic photon flux density (PPFD) of 60 μmol m–2 s–1 with either a low or a high red:far-red light ratio (LR and HR, repectively). The chambers were supplied with air containing
CO2 at a concentration of either 400 (LR4 and HR4, respectively) or 800 μmol mol–1 (HR8 and LR8, respectively). After 4 months, leaf morphology and photosynthetic characteristics were determined. Relative
to HR4, the LR4 treatment increased leaf area and total chlorophyll concentration (Chl) by 24 and 25%, respectively, but reduced
leaf mass per unit area (LMA) by 19%. Elevated [CO2] significantly increased leaf area and LMA but did not affect Chl of LR or HR plants. Leaf nitrogen concentration was unaffected
by the red:far-red light ratio but decreased significantly in seedlings in the elevated [CO2] treatment. Photosynthesis measured in situ under the growth conditions of ambient light and [CO2] (Aamb) was 30% lower on an area basis and 14% lower on a mass basis in LR4 plants than in HR4 plants. Elevated [CO2] reduced the activity of ribulose-1,5-bisphosphate carboxylase/oxygenase and thus decreased light-saturated photosynthetic
rate in both HR and LR plants. Elevated [CO2] increased mean leaf area and decreased respiration rates in both LR and HR plants. The LR8 plants had significantly higher
Aamb than LR4 plants, but similar Aamb to HR8 plants.
Keywords:
carboxylation activity, chlorophyll, leaf area, nitrogen, spectral quality, stomatal conductance.
