Interactions between light and temperature on the physiological ecology ofGracilaria tikvahiae (Gigartinales: Rhodophyta) |
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Authors: | B. E. Lapointe K. R. Tenore C. J. Dawes |
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Affiliation: | (1) Skidaway Institute of Oceanography, P.O. Box 13687, 31406 Savannah, Georgia, USA;(2) Biology Department, University of South Florida, 33620 Tampa, Florida, USA;(3) Present address: Harbor Branch Institution, Inc., P.O. Box 818, 33043 Big Pine Key, Florida, USA |
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Abstract: | Main effects and interactions of light and temperature on rates of growth (), net photosynthesis (Ps), and dark respiration (R) of the red seaweedGracilaria tikvahiae were investigated in outdoor, nutrient-replete continuous-flow seawater culture chambers. Below 15°C,G. tikvahiae did not grow and between 15° and 30°C, both main effects and interactions of light and temperature on and Ps were significant, which explains the occurrence of this alga as a summer annual in its northern range. Temperature interacted with light (I) through its influence on the vs I and Ps vs I curves. The initial slope of the vs I curve, , the light saturation intensity, Is, and maximum growth rate, max, were all significantly lowerat 15°C compared to 20°, 25°, or 30°C. Maximum values of max, the Ps:R ratio and the net photosynthesis:gross photosynthesis ratio (Ps:Pg) all occurred at 25°C, suggesting that this is the best temperature for growth ofG. tikvahiae. Values for Pmax increased up to 30°C, indicating that the temperature for maximum growth and net photosynthesis are not the same forG. tikvahiae. Significant photoinhibition of growth and photosynthesis at full incident sunlight (I0) occurred at 15°C but not at 20°, 25°, or 30°C. Steele's equation fit the 15°C vs I data best, whereas the hyperbolic tangent function fit the 20°, 25°, and 30°C data best. Main effects and interactionof light intensity and temperature on rates of R were also significant (P<0.001). R was highly intercorrelated with and Ps (0.86r0.94), indicating that R inG. tikvahiae is primarily regulated by growth rate and not temperatureper se. Environmental factors that regulate growth, such as light intensity, exert a great influence on R inG. tikvahiae. |
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