The photosynthetic and respiratory physiology of Palmaria palmata (L.) Stackhouse, as affected by temperature, irradiance, total carbon dioxide, salinity and pH

Abstract

A chamber of variable volume was designed in which photosynthesis and respiration of the red alga Palmaria palmata could be measured under a variety of environmental conditions. The chamber was equipped with a polarographic oxygen electrode, pH electrode, injection port, and a sample removal tube. Using this apparatus, the effects of temperature, irradiance, total carbon dioxide concentration, salinity, and pH on the photosynthetic and respiratory rates of intact P. palmata plants were measured. The photosynthetic rates of seasonally adapted plants showed relatively little variation and no seasonal changes in respiration were detectable. P. palmata was shown to be a stenothermal plant, with a temperature optimum for photosynthesis of 10 and 15°c . . The photosynthetic rate became light saturated above 212 microEinsteins, with Pmax being temperature dependent. The compensation point for plants in late winter was found to be approximately 6.6 microEinsteins. Ambient sea water concentrations of inorganic carbon were shown to be insufficient to produce a maximum photosynthetic rate. By raising the concentration of total carbon dioxide to 6.0 - 7.0 mM, it was possible to stimulate photosynthesis by about 2.7 fold over the rate at normal concentrations. Maximum rates for photosynthesis and respiration were observed at a salinity of 32.0°/oo. A pH of 6.5 to 7.5 stimulated photosynthesis when compared to rates at pH 8.1, but below pH 6.5 photosynthesis dropped off sharply. At pH values above 8.0, a nearly linear decrease in the photosynthetic rate was observed.