Photosynthetic carbon assimilation by Crassula helmsii |
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Authors: | Jonathan R Newman John A Raven |
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Institution: | (1) Department of Biological Sciences, University of Dundee, DD1 4HN Dundee, Scotland;(2) Present address: Department of Agricultural Sciences, BBSRC Institute of Arable Crops Research, Long Ashton Research Station, Centre for Aquatic Plant Management, University of Bristol, Broadmoor Lane, Sonning-on-Thames, RG4 0TH Reading, Berkshire, UK |
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Abstract: | Photosynthesis of Crassula helmsii, an amphibious aquatic macrophyte weed species, has been measured with respect to pH and irradiance. C. helmsii shows a marked diel fluctuation in titratable acidity, which can be accounted for by changing levels of malic acid. C. helmsii is unable to use HCO
inf3
sup-
for photosynthesis and exhibits generally low photosynthetic rates when CO2 is not limiting. The photon flux density at which the onset of light saturation of photosynthesis is reached (E
K
) is low for aquatic macrophytes. Some advantages conferred on C. helmsii by the possession of crassulacean acid metabolism are an extension of the period of assimilation of dissolved inorganic carbon, resulting in a reduction in the limitation imposed on photosynthesis in aquatic environments by a very high CO2 diffusion resistance. |
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Keywords: | Aquatic macrophyte Crassulacean acid metabolism Nuclear magnetic resonance |
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