Abstract
Techniques are described for measuring gas exchange in seaweeds held in moist air (air suspension). In the species we have examined, oxygen has little or no effect on photosynthesis except at very low (50 μ1·1 −1) CO 2 concentration. Photorespiration could not be detected unless the seaweeds were treated simultaneously with high O 2 and low CO 2 or with the carbonic anhydrase inhibitor, diamox. However, sporulating and meristematic tissues exhibit oxygen-insensitive light respiration (CO 2production in light not associated with photorespiratory metabolism). Elevated pH in the surface water of seaweeds also caused light respiration. Oxygen-sensitive wound respiration was observed that could easily be mistaken for photorespiration. C 4 photosynthesis could not be detected. On the basis of several experimental approaches it was concluded that these seaweeds normally absorb bicarbonate rather than CO 2 from sea water. High CO 2 concentrations are required in gas streams aerating seaweed cultures in air or water suspension to maintain the bicarbonate concentration at levels normally found in sea water and to support normal levels of photosynthesis.
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