Photoacclimation of Ulva rotundata (Chlorophyta) under natural irradiance |
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Authors: | W J Henley J Ramus |
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Institution: | (1) Marine Laboratory, Duke University, 28516-9721 Beaufort, North Carolina, USA;(2) Department of Botany, Duke University, 28516-9721 Beaufort, North Carolina, USA |
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Abstract: | Two vegetative clones (designated 11/85 and 7/86 in accordance with month/year of collection) of the green macroalga Ulva rotundata were collected in the vicinity of Beaufort, North Carolina, USA. Each was grown in an outdoor continuous-flow system in summer (20°C) of 1986 and late winter (10° to 17°C) of 1987, in irradiances ranging from 9 to 100% of full sunlight, with and without NH
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enrichment. Continuous enrichment of influent estuarine water (dissolved inorganic nitrogen 2 M, N:P5) to 8–12 M NH
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had only a slight effect on growth rate. Temperature changes of 2 to 3°C had a much greater effect. Prolonged exposure to a given daily irradiance resulted in acclimation, exposure to a given daily irradiance resulted in acclimation, indicated by faster growth of conditioned plants relative to those transferred from a different irradiance. Most of the difference in growth rates between transferred and control plants was attributed to differences in thallus absorptance. Growth was photoinhibited above 40% sunlight at temperatures below 15°C, but not above 20°C. Following interday irradiance transfers, thallus percent dry weight changed in a manner that suggests different response times for photosynthesis and cell division. |
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