해수의 CO2와 영양염 농도 및 조도가 구멍갈파래(Ulva australis) 배아, 유엽과 성체의 생장에 미치는 영향

Abstract

The effects of CO2 concentration, nutrient levels, and irradiance on the growth of germlings and juveniles, and on the photosynthesis of adults were examined in a green tide alga, Ulva australis. We used a factorial experimental design with two CO2 concentrations (380 and 750 ppm), two nutrient levels (control and PES medium), and two irradiance levels (50 and 100μmol photons m−2s−1 ). Germlings grew best ( 664.15±61.45μm in length) under conditions of 750 ppm, PES, and 100μmol photons m−2s−1 after 10 days in culture. Relative growth rates (RGR) of the juveniles were greatest (4.41% day−1 ) under conditions of 750 ppm, PES, and 50μmol photons m−2s−1 after 5 days in culture. Photosynthetic efficiency ( Fv/Fm ) of the adult discs was 0.73±0.05 before the experiment and reached a maximum ( 0.83±0.01 ) under conditions of 750 ppm, control, and 50μmol photons m−2s−1 after 5 days in culture. Growth (germlings and juveniles) and photosynthesis (adult discs) of Ulva australis increased when CO2 levels were 750 ppm. Additionally, the optimal irradiance for growth and photosynthesis differed among stages, wherein germlings grew best at 100μmol photons m−2s−1 , juveniles grew best at 50μmol photons m−2s−1 , and adults photosynthesized most at 50μmol photons m−2s−1 . The performance of Ulva australis at all examined life stages was enhanced under the PES nutrient treatment. In conclusion, the physiological responses of U. australis to varying CO2 , nutrient, and irradiance levels differed slightly among life stages. However, growth and photosynthesis always increased with elevated CO2 and nutrient concentrations. These results indicate that U. australis green tide blooms might occur more frequently in coastal areas if CO2 and nutrient concentrations increase.