Biological Adaptation Of Gracilaria Lemaneiformis And Pyropia Haitanensis Affected By Ocean Acidification

Marine macroalgae perform great potential for biomass production and CO2 bioremediation, which are important for remitting the global climate change. Rising CO2 in atmosphere resulted in carbonate and p H level changes in seawater. Acidified seawater and increasing temperature caused by rising CO2 exert strong effects on marine macroalgae, such as physiological status and chemical components of seaweeds.In these studies, the economical macroalgae Gracilaria lemaneiformis and Pyropia haitanensis that were mainly maricultured in South China sea, were employed to investigate the physiological and morphological responses of these two red algae to ocean acidification(OA) and the coupling effects of rising CO2 and other environmental factors(such as light intensity, nutrient, and heavy metal) under laboratory conditions; and the interspecific competition between G. lemaneiformis and Ulva lactuca was also estimated. These were aiming to provide important theoretical foundations and technical supports for seaweed cultivation and ecological security management along the coastal under climate change.The immediate photosynthetic responses results of G. lemaneiformis and P. haitanensis to acidified seawater(On the basis of the predicted scenario of elevated CO2 levels from 390 μL?L-1 to 1,000 μL?L-1, the p H in seawater decreased from 8.17 to 7.78) indicated that, during 2 h acidifying treatment, the photosynthesis of G. lemaneiformis was firstly enhanced, and then was depressed. However, the light resistance ability of this algae was hardly influenced. The maximum relative electron transport rate(r ETRm) and apparent photosynthetic efficiency(α) in P. haitanensis were depressed in the first 1 h, and then recovered. Conversely, the light resistance of P. haitanensis was enhanced by acidified seawater within 1 h. When the two algae were introduced into acidified seawater, they still had relative high r ETRm and photochemical efficiency within a short time.Although there was also fewer biomass accumulation in G. lemaneiformis under high temperature condition(the last phase of maricultivation), the yield of harvest of the alga was relatively reduced as compared to other maricultivation phases. Acidified seawater enhanced growth of G. lemaneiformis under high temperature, but declined the amino acid content. High light intensity and acidification enhanced the biomass accumulation in G. lemaneiformis under high temperature, but lowered its nutritional quality. Under low light intensity, the dry weight of the alga was relatively lowered because of the high water content in thalli.The results of the study on interspecific competition between G. lemaneiformis and Ulva lactuca showed, that U. lactuca exhibited a relatively higher growth rate and maximum net photosynthetic rate than G. lemaneiformis under both the two CO2 levels, and had a relatively higher efficiency in light utilization. Growth and photosynthesis of G. lemaneiformis were inhibited in the presence of U. lactuca. This inhibition of G. lemaneiformis was more severe when it was grown under elevated CO2 levels. When U. lactuca was bicultured, elevated CO2 levels caused a significant increase in light harvesting efficiency and maximum quantum yield. The interspecific competition between G. lemaneiformis and U. lactuca was most probably due to the rapid growth of U. lactuca. We believe that, on the basis of the predicted scenario of elevated CO2 levels, the epiphyte U. lactuca would presumably have greater negative impacts on G. lemaneiformis maricultivation; therefore, more labor would be required to reduce the epiphytization of this species during G. lemaneiformis mariculture.The growth and physiological responses of P. haitanensis to CO2 levels were largely dependent on the nutrients supplement in the seawater. Elevated CO2 significantly enhanced P. haitanensis growth and NO3--uptake, but lowered the p H compensation points, regardless of nutrient levels, and enhanced photosynthesis and α when the nutrient levels were high. However, CO2 had little effect on photosynthetic rates at low nutrient levels. At each nutrient level, CO2 elevation lowered both the phycobiliproteins(PB) and soluble protein contents(SP), but enhanced biomass accumulation. Chlorophyll a(Chl a) and carotenoid(Car) contents were markedly increased by high CO2 concentrations at low nutrient levels. Increasing nutrient supply significantly enhanced growth, p H compensation points and photosynthesis in P. haitanensis at each CO2 level. However, the differences of the effects between intermediate and high nutrient levels on this algae were not significant for photosynthesis, pigment contents, and nutrient uptake, regardless of CO2 levels.The results of coupling effects of CO2 levels and soluble iron in seawater displayed that, elevated CO2 increased the Chl a and soluble carbonhydrate(SC) contents in P. haitanensis, and increased the ratio of SC/SP, but declined the SP content. The Fe enrichment in seawater, including Fe(II)-EDTA and Fe(III)-EDTA, enhanced the optimal photochemical yield of PSII and other chlorophyll fluorescence parameters in this alga, and finally enhanced its photosynthetic rate and growth. High CO2 level enhanced iron uptake, and iron enrichment outstandingly enhanced the growth and photosynthesis of P. haitanensis. Moreover, the SC content and the ratio of SC/SP were also increased by iron enrichment under high CO2 level. Increased SC fundamentally meet the demands of energy for algal tissue organizing and growth, and this was intuitively reflected by respiration.Enrichment of CO2 was mainly benefit to the resistance to bacterial red-rotting disease in P. haitanensis at relative low light condition. CO2 elevation in culture medium offered sufficient DIC for the diseased alga as the CO2 dissolved into seawater, this increased the compounding of photosynthetic pigments, and enhanced the photosynthesis in P. haitanensis. The diseased alga might resist the disease with increased ability by taking advantage of sufficiently compounded components.In conclusion, the immediate chlorophyll fluorescence responses of economical macroalga G. lemaneiformis were not completely same as P. haitanensis when they were introduced into acidified seawater. The effects of OA(CO2 enrichment) on photosynthesis and other physiological metabolism in these two algae were generally influenced by other environment factors. Once the nutrient and light conditions were suitable, photosynthesis and growth of the two algae would be enhanced by OA. As the global climate change continues, the maricultured G. lemaneiformis would be strongly impacted by epiphyte species U. lactuca, and the quality of G. lemaneiformis would be negatively influenced by high temperature in the last phase of maricultivation. However, increasing of soluble iron in acidified seawater would be benefit to P. haitanensis photosynthesis and growth. These results implied that the effects of ocean acidification on macroalgal growth and physiological metabolism should be conducted under multiple environmental factors.