ISSN:
1432-1793
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract Six marine macroalgae and two angiosperms were examined for their ability to use HCO 3 - and CO2 for photosynthesis. All species used HCO 3 - despite wide taxonomic differences. They also used HCO 3 - with high affinity: natural HCO 3 - concentrations (2.2 mM) were close to saturation, and the apparent half-saturation constants were low, i.e. K1/2 (HCO 3 - )=0.54 to 0.80 mM HCO 3 - . Expressed as a ratio, the affinity for CO2 relative to HCO 3 - under rate-limiting concentrations was about 2 for the marine species compared to much higher values, 5.4 to 101, among freshwater species examined previously. This difference was due to a higher affinity for HCO 3 - among marine species, whereas the affinity for CO2 was in the same range for marine and freshwater species, i.e. K1/2 (CO2)=0.08 to 0.30 mM. The high affinity for HCO 3 - of marine species is consistent with the high and constant availability of HCO 3 - and the low availability of CO2 in seawater. In freshwaters, availability of HCO 3 - and CO2 varies considerably, depending on habitat. The difference in HCO 3 - affinity may be due to different electrogenic ionpumps and thus mechanisms of HCO 3 - -use, operating in freshwater and marine species. Photosynthetic rates in natural seawater were close to maximum at atmospheric equilibrium (pH 8.2 to 8.4) and declined at high pH approaching zero between pH 9.5 and 10.5. This reduction may be due to the conversion of HCO 3 - to CO 3 - , followed by CaCO3 precipitation, and/or to a direct pH-effect. Ulva lactuca and Enteromorpha sp. retained photosynthetic activity at the highest pH tested (10.5), consistent with the high pH recorded in mats of these species.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00392819
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