title: Variable HCO3-affinity of Elodea canadensis Michaux in response to different HCO3-and CO2concentrations during growth.
abstract: Elodea canadensis grows over a wide range of inorganic carbon, nutrient, and light conditions in lakes and streams. Affinity for HCO3-use during photosynthesis ranged from strong to weak in Elodea collected from seven localities with different HCO3-and CO2concentrations. The response to HCO3-was also very plastic in plants grown in the laboratory at high HCO3-concentrations and CO2concentrations varying from 14.8 to 2,200 μM. Bicarbonate affinity was markedly reduced with increasing CO2concentrations in the growth medium so that ultimately HCO3-use was not detectable. High CO2concentrations also decreased CO2affinity and induced high CO2compensation points (360μM CO2) and tenfold higher half-saturation values (∼800 μM CO2).The variable HCO3-affinity is probably environmentally based. Elodea is a recently introduced species in Denmark, where it reproduces only vegetatively, leaving little opportunity for genetic variation. More important, local populations in the same water system had different HCO3-affinities, and a similar variation was created by exposing one plant collection to different laboratory conditions.Bicarbonate use enabled Elodea to photosynthesize rapidly in waters of high alkalinity and enhanced the carbon-extracting capacity by maintaining photosynthesis above pH 10. On the other hand, use of HCO3-represents an investment in transport apparatus and energy which is probably not profitable when CO2is high and HCO3-is low. This explanation is supported by the findings that HCO3-affinity was low in field populations where HCO3-was low (0.5 and 0.9 m M) or CO2was locally high, and that HCO3-affinity was suppressed in the laboratory by high CO2concentrations.
authors.affiliation: Freshwater Biological Laboratory, University of Copenhagen, Helsingørsgade 51, DK-3400, Hillerød, Denmark.
authors.forename: Kaj
authors.initials: K
authors.lastname: Sand-Jensen
authors.affiliation: Freshwater Biological Laboratory, University of Copenhagen, Helsingørsgade 51, DK-3400, Hillerød, Denmark.
authors.forename: David M
authors.initials: DM
authors.lastname: Gordon
keywords: Aquatic plants; Eloded canadensis; HCO 3 - /CO2 concentration; Photosynthesis