Effects of circadian rhythms of fluctuating temperature on growth and biochemical composition of Ulva pertusa
The marcoalga Ulva pertusa was cultured under (20 ± 2)°C, (20 ± 4)°C, (20 ± 6)°C, (20 ± 8)°C and (20 ± 10)°C circadian rhythms of fluctuating temperature conditions, and constant temperature of 20°C was used as the control. The growth rate of macroalga at (20 ± 2)°C, (20 ± 4)°C and (20 ± 6)°C were significantly higher than that at constant temperature of 20°C, while growth rate at (20 ± 8)°C and (20 ± 10)°C were significantly lower than that at constant temperature of 20°C. The growth rate of macroalga was a quadratic function of the thermal amplitude. Such a growth model can be described by G = β 0 + β 1(TA) + β 2(TA)2, where G represents the relative growth rate, TA is thermal amplitude in degree Celsius, β 0 is the intercept on the G axis, and β 1 and β 2 are the regression coefficients. The optimal thermal amplitude for the growth of thallus at mean temperature of 20°C was estimated to be ± 3.69°C. Analysis of biochemical composition at the final stages of thaulls growth revealed that diel fluctuating temperature caused various influences (P < 0.05). The content of chlorophyll, protein and total solute carbohydrate at (20 ± 2)°C and (20 ± 4)°C were slightly higher than those at constant temperature of 20°C, however no statistically significant differences were found among them (P > 0.05). While osmolytes (total solute carbohydrate and free proline) at (20 ± 10)°C were significantly higher than that at 20°C (P < 0.05). Therefore, more chlorophyll and carbohydrate production might account for the enhancement in the growth of macroalga at the diel fluctuating temperatures in the present study.
KeywordsMacroalga Ulva pertusa Fluctuating temperature Growth Biochemical composition
The authors thank Prof. Taniguchi for his kind supply of the axenic nonsexual strain of U. pertusa, and Dr. Yunwei Dong and Xidan Zhao providing assistance in the care and maintenance of the experiment. This work was supported by National Eleventh Five-year Scientific and Technological Key Project (Grant No. 2006BAD09A01) and Hi-Tech Research and Development Program of China (Grant No. 2006AA10Z409).
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