Licht-im-Terrarium: Literaturdatenbank
Licht-im-Terrarium: Literaturdatenbank |
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Chazdon, R. L. (1986). Light variation and carbon gain in rain forest understorey palms. Journal of Ecology, 74(4), 995–1014. Added by: Sarina (2012-01-22 18:56:30) |
| Resource type: Journal Article BibTeX citation key: Chazdon1986 View all bibliographic details  |
Categories: Englisch = English Keywords: Sonne = Sun, Spektrum = Spectrum Creators: Chazdon Collection: Journal of Ecology |
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| Abstract |
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(1) The consequences of light variation for daily carbon gain in three understorey palm species are described. Detailed measurements of photosynthetic photon flux density (PPFD) were made in closed-canopy understorey, gap-edge and gap-centre sites to determine the range of light conditions. Based on these results and the responses of seedlings grown in full shade, computer simulations were used to compute total daily leaf carbon gain. (2) Median daily total PPFD in gap-edge habitats was 1-1.5 mol m-2, compared with 0.26-0.33 mol m-2 in adjacent understorey sites. Median daily PPFD in the gap centre increased with gap size. In the understorey, more than 80% of averages calculated for 5-min periods were below 10 μ mol m-2 s-1, whereas most readings in the centre of a 150-m-2 gap were between 50-100 μ mol m-2 s-1 and along the gap edge 20-50 μ mol m-2 s-1. (3) For Asterogyne martiana and Geonoma cuneata, two dwarf species, median daily total PPFD did not increase from ground level to 1.5 m. Fifty per cent of all PPFD measurements below 1.5 m were between 0.18-0.39 mol m-2. At crown heights above 1.5 m, median daily total PPFD increased to 0.51 mol m-2. Within clones of G. congesta, daily total PPFD increased significantly with crown height; median PPFD incident on crowns 3.5-4.0 m tall was five times greater than PPFD at heights below 1.4 m. (4) On sunny days, the proportion of daily total PPFD contributed by sunflecks ranged from 10% to 78%. The relative proportion of daily PPFD contributed by sunflecks increased as the PPFD of background diffuse radiation decreased. (5) Photosynthesis of seedlings grown in full shade did not differ significantly among the three species. Light compensation points of full-shade-grown plants were between 3-4 μ mol m-2 s-1, and light-saturated photosynthetic rates measured as CO2 uptake were between 3 and 4 μ mol m-2 s-1. Light saturation occurred between 200 and 400 μ mol m-2 s-1. (6) Carbon gain simulations of full-shade-grown seedlings indicate that a positive carbon gain over 24 h occurs at PPFD greater than 0.20 mol m-2. When most of the total daily PPFD was in the form of diffuse radiation, total daily carbon gain was linearly related to total daily PPFD. Daily carbon gain was not a simple function of daily total PPFD when sunflecks contributed more than 50% of the total quantum flux. On days with sunny periods, the proportion of total daily carbon gain during sunflecks ranged from 15% to 60%. (7) Seedlings of the three species grown in the gap edge had higher rates of leaf production, were taller and had larger leaves than seedlings grown in a closed-canopy understorey site. Measurements of growth and photosynthesis, and carbon-gain simulations suggest that light conditions along gap edges and within small gaps are ideal for these species. Added by: Sarina |