Relationships between irradiance and photosynthesis for marine benthic green algae (Chlorophyta) of differing morphologies |
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Authors: | Keith E Arnold Steven N Murray |
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Institution: | Department of Biological Science, California State University, Fullerton, CA 92634, U.S.A. |
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Abstract: | Photosynthesis-irradiance relationships were determined in the field for five species of littoral and shallow sublittoral marine benthic green algae (Chlorophyta) of differing morphologies. Each species exhibited a linear increase in photosynthetic rate with increasing irradiance up to a maximum light-saturated value. Full sunlight (1405 to 1956 μE·m?2·s?1) inhibited photosynthesis of all species except the thick, optically dense, Codium fragile (Sur.) Har. Compensation irradiances ranged from 6.1 μE·m?2·s?1 for Enteromorpha intestinalis (L.) Link to 11.4 μE·m?2·s?1 for Ulva lobata (Kütz) S. & G. and did not reveal a consistent relationship to seaweed morphology. Saturation irradiances were determined statistically (Ik) and visually from graphical plots. with the latter technique resulting in values three to eight times higher and different comparative rankings of species than the former. Ik saturation irradiances were highest for Chaetomorpha linum (Müll.) Kütz. (81.9 μE·m?2·s?1) and lowest for Codium fragile (49.6 μE·m?2·s?1) and did not reveal a relationship with seaweed morphology. Regression equations describing light-limited photosynthetic rates and the relative magnitudes of the maximal net photosynthetic responses both strongly suggested a relationship with seaweed morphology. Highest net photosynthetic rates were obtained for the thin, sheet-like algae Ulva lobata (9.2 mg C·g dry wt?1·h?1), U. rigida C. Ag. (6.5 mg C·g dry wt?1·h?1) and the tubular form, Enteromorpha intestinalis (7.3 mg C·g dry wt?1·h?1), while lowest rates occurred for Codium fragile (0.9 mg C·g dry wt?1·h?1). Similarly, steepest light-limited slopes were found for the algae of simpler morphology, while the most gradual slope was determined for Codium fragile, the alga with greatest thallus complexity. |
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