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Photosynthetic Gas Exchange Responses of Australian Tropical Forest Trees in Canopy, Gap and Understory Micro-Environments

R. W. Pearcy
Functional Ecology
Vol. 1, No. 3 (1987), pp. 169-178
DOI: 10.2307/2389419
Stable URL: http://www.jstor.org/stable/2389419
Page Count: 10
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Photosynthetic Gas Exchange Responses of Australian Tropical Forest Trees in Canopy, Gap and Understory Micro-Environments
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Abstract

The photosynthetic responses of three tropical tree species were investigated in the contrasting micro-environments of the canopy, a gap and the understory of a tropical forest in north-eastern Australia. Measurements were made with a small transportable field gas exchange apparatus on the evergreen species Argyrodendron peralatum (F.M. Bailey) Edlin ex I.H. Boas and Castanospermum australe (Cunn.) Frazer and Cook, which regenerate in the understory and the deciduous gap species Toona australis (F. Muell.) Harms. Acclimation to the prevailing light environment was evident in all species, with the canopy leaves having higher light saturated photosynthetic rates, dark respiration rates and stomatal conductances than the understory leaves. For A. peralatum, leaves in the gap were generally intermediate between those in the canopy and understory. There was no evidence for acclimation to the differences in temperature or leaf-air vapour pressure deficits between the canopy and understory leaves. Determinations of the daily courses of CO2 uptake showed that although the daily photon flux density (PFD) in the understory was only 3% of that at the canopy top, leaf carbon gain was nearly 10% of that measured for the canopy leaf. In the understory, photosynthesis during sunflecks accounted for about one third of the daily carbon gain. There was no evidence that temperatures or leaf-air vapour pressure deficits significantly limited CO2 uptake in the canopy.

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