Physiological Ecology of the Brown Alga Phaeostrophion irregulare Setchell et Gardner: II Macroscopic Plants

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Abstract
The apparent photosynthesis of the macroscopic plants of P. irregulare is light saturated at .apprx. 700 ft-c. The blades are the main photosynthetic organs of the plant as their rate of photosynthesis is much greater than that of the holdfast. The optimum temperature for photosynthesis for the blades and holdfasts is .apprx. 13.5.degree. C, but a high rate of photosynthesis occurs over a wide range of temperatures. The respiration of the blades and holdfast is very low and it may be of some adaptive advantage to the plant in sandy habitat where it grows abundantly. Neither respiration nor apparent photosynthesis of the blades is conspicuously different between 20-40.permill.. The macroscopic plants are more tolerant than the juvenile stages to a wide range of temperature, salinity and desiccation conditions. Overall, the temperature and salinity tolerances of the macroscopic plants appear to be much greater than that required in nature, but this does not appear to be the case for resistance to dessication. Apparently, the blades often die after a dehydration of 40-60%. The holdfasts of P. irregulare seem to be more resistant than the blades to extreme conditions.