| According to the latest data of the World Meteorological Organization (WMO)showed that the concentration of CO2in the atmosphere increased to391ppm in2011from pre-industrial value about280ppm. CO2concentration rising not only leads to thegreenhouse effect, but also a direct result of ocean acidification. Recently, researchersare looking for the best way of CO2reduction and method of prevention oceanacidification. Studies have shown that marine macroalgae plays an important role inatmospheric CO2abatement and reduction of seawater dissolved inorganic carbon (DIC)content through photosynthetic carbon fixation. But it is not good for nothing thatoutbroken large-scale green tide in China’s Yellow Sea for8consecutive years. Greentide algae has the characteristics of fast growth, it can obsord nitrogen, phosphorus,carbon, and other important elements of seawater during the growth process, and at thesame time the atmospheric CO2is absorbed at a high level that can prevent marineeutrophication and ocean acidification. But this research that effects of ecologicalfactors on Ulva prolifera carbon fixation and associated changes to seawater pH, as wellas the determination of seawater inorganic carbon system parameters in green tideoutbreaks areas has been few studied.Therefore, Ulva prolifera which is dominant species of green tide in Yellow Sea,has been chosen as the research object in this paper. Firstly, the effects of nitrogen andphosphorus enrichment on the growth and photosynthetic carbon assimilation in U.prolifera were investigated. Four nitrogen and phosphorus treatments were set up, highnitrogen and high phosphorus (HNHP), high nitrogen and low phosphorus (HNLP), lownitrogen and high phosphorus (LNHP) and low nitrogen and low phosphorus (LNLP).The measurements were carried out on the growth rate, chlorophyll fluorescenceparameters, photosynthetic rate and the absorption of dissolved inorganic carbon (DIC)in U. prolifera. In addition, we discussed the effects of temperature and irradiance oncarbon fixation by U. prolifera and associated changes to seawater pH. The thalli werecultured under six temperature gradient groups (10,15,20,25,30,35°C) and sevenirradiance gradient groups (20,40,60,80,100,150,200μmol·m-2·s-1) within48hours.Finally, we determined chlorophyll fluorescence parameters (sach as Fv/Fm,PSII, Fv/F0, NPQ, rETR, ect.), chlorophyll content, Rubisco activity and photosynthetic rate of U. prolifera. And seawater DIC content, including-,2-, CO2(T), and pH changesin green tide outbreaken area were investigated. Combining with the results of thelaboratory study, we assessed the fixed carbon content of green tide algae. We havethese conclusions as follows:Nitrogen (N) and phosphorus (P) enrichment promoted the growth of U. proliferaas well as its photosynthetic carbon assimilation, therefore increasing the pH value ofseawater.1) N and P enrichment significantly promoted the relative growth rate of U.prolifera (p <0.05). The relative daily growth rate with the HNHP treatment was1.55times greater than with the LNLP treatment.2) The chlorophyll fluorescence parametersall reached their maximum values under the HNHP treatment, and, compared to theLNLP treatment, the differences were significant (p <0.05).3) Either N or P enrichmentcould increase the photosynthetic rate of thalli (p <0.05). The photosynthetic rate underthe HNHP treatment was the highest (114.0μmol()·g-1(FW)·h-1), which was1.52times that of LNLP treatment.4) N and P enrichment promoted the ability of U.prolifera to absorb DIC from the seawater, thus increasing the pH value of the seawater.The DIC absorption ability was the strongest under the HNHP treatment, with anabsorption rate of0.70mmol·L1, which was1.63times greater than under the LNLPtreatment (p <0.05). Algae under the HNHP treatment caused the greatest increase inseawater pH values, by a margin of1.43, which was1.40times that under the LNLPtreatment (p <0.05).The effects of temperature and irradiance on the photosynthetic carbon fixation ofthe thalli and associated changes of seawater pH were highly significant (p <0.01). At60μmol m-2s-1and20~30°C, the thalli exhibited high carbon sequestration rate[.~.01μmol()·g-1(FW)·h-1]. Especially at25°C, the highest carbon fixationrate of53.01μmol g-1FW h-1and the fastest seawater pH elevation rate of0.075g-1FW h-1in the temperature gradient experiments. At20°C, the optimal irradiance for U.prolifera carbon fixation and associated changes of seawater pH was100μmol·m-2·s-1,the highest rates were. μmol g-1FW h-1and0.086g-1FW h-1, respectively, in theirradiance gradient experiments. The optimal combination of temperature and irradiancewas25°C and100μmol m-2s-1, and the highest rates were.10μmol g-1FW h-1and0.091g-1FW h-1, respectively, under these conditions.It was healthy when U. prolifera floated to Binhai sea area, and it has strongabsorptive capacity for DIC, can promote seawater inorganic carbon system circulation,improving the sea water pH.1) Fv/Fm,PSII, Fv/F0, NPQ, rETRmaxwere0.67,0.57,2.16,0.34,88.40, respectively. Chlorophyll a (Ca), chlorophyll b (Cb), total Chlorophyll(CT) content were0.91,0.65,1.56mg·g-1, respectively. Ca/Cbwas1.40. Rubisco activity was11. μmol(CO2)·g-1(FW)·min-1.2) Seawater inorganic carbon systemparameters in different area of the thalli coverage showed that different degrees ofchanges. From the edge of coverage to covered centre, DIC and-concentrationswere decreased, and there was a significant difference (p <0.05). At the same time,these values were much lower than that uncovered region. pH values graduallyincreased from the uncovered region to covered center (p <0.05). And the highest valuewas8.52in covered center.3) Green tide algae biomass totaled98.328million tons wetweight from2008to2013. And they can fix18.4367million CO2. If we go according to15yuan/ton CO2to levy, the carbon tax could be reduced276million yuan. To someextent, the will decrease taxpayers’ pressure, thereby disaster will be turn into greenweath. |
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