Photosynthetic Characteristics Of Gracilaria Chouae In The Seawater Of Acidification And Heavy Metal

Gracilaria chouae,a kind of large marine algae,belongs to Rhodophyta and considered as important economic algae in coastal region of south China.Beacause of its fast growth,rich in nutritional value,and its crisp taste,easy to digest,it is widely used as high quality food to abalone.Despite its enormous economical potential,the cultivation of G.chouae is still in the initial stage in north China.In the research,almost research focuses on the value of its component,physiological characteristics and technology in pond cultivation.Today,environmental pollution and climate change have become an important factor affecting healthy and sustainable development algal aquaculture industry.It is urgent to analyze the photosynthetic characteristics and inorganic carbon utilization mechanism of G.chouae.We investigated the mechanism of photosynthesis characteristics and DIC utilization in Gracilaria chouae and its changes in different environments.In the period of October 2015 to November 2016,we started our experiments in Yellow Sea Fisheries Research Institute and National Engineering and Research Center of Marine Shellfish.The main contents include the following aspects: 1.Used PAM to learn and compare photosynthetic characteristics of G.chouae and Gracilaria lemaneiformis.2.Investigated CO₂ concerntrating mechanism of G.chouae.3.Studied on the impact of photosynthetic changes on G.chouae at seawater with different carbonate system based on the result by experiment two;4.Effects of Hg²⁺ and Pb²⁺ on the growth and photosynthetic physiological characteristics of Gracilaria chouae.The main results were as follows:1.Studies on photosynthetic characteristics of G.chouae and G.lemaneiformis.Under optimal condition,the chlorophyll fluorescence parameters showed that Fv/Fm and Y???of G.chouae which means efficiency of light energy conversion in PS? and photochemical quenching?q L?were significantly higher than that of G.lemaneiformis?P<0.05?,and non-photochemical quenching?NPQ?was found no significant difference between G.lemaneiformis and G.chouae?P>0.05?,which indicated that G.chouae distributes more energy in photosynthesis.The data of Ik and Pmax on G.chouae were significantly higher than it on G.lemaneiformis,which indicated that G.chouae has greater tolerance of higher illumination.The P-C curve of photosynthesis rate showed that when the inorganic carbon concentration reached 8.8 mmol·L-1,G.chouae reached the peak in photosynthesis rate,which indicated that of normal seawater inorganic carbon concentration did not reach saturation state of G.chouae.2.We detected the changes of pH compensation point of G.chouae in seawater with different temperature and different inhibitors.The results showed that extracellular carbonic anhydrase was the main catalytic material under 10? and 15?.And intracellular carbonic anhydrase mainly controlled the absorbtion of DIC in G.chouae in temperature of 20,25,30?.Photosynthetic O₂ evolution rate of G.chouae in three kind of pH?6.5,8.1,9.0?with different inhibitors showed that the photosynthetic rate in pH 6.5 seawater was significantly higher than that in pH 8.1 and 9.0 seawater?P<0.05?.The photosynthetic rate of EZ treatment and AZ treatment was significantly lower than control group and DIDS treatment?P<0.05?,which indicated that G.chouae has the ability of HCO3-utilization.3.DIC utilization mechanism of G.chouae in acidified seawater.We detected the pH compensation point,photosynthetic O₂ evolution rate,pH changes and DIC utilization of G.chouae in natural sweater?pH 8.1?,HCl modified seawater?pH 7.7?and CO₂ modified seawater?pH 7.7?.The result showed that pH compensation point were greater than 9.0 in all treatment and natural seawater > HCl modified seawater > CO₂ modified seawater.The photosynthetic O₂ evolution rate of G.chouae in HCl modified seawater was significantly lower than that of other treatment?P<0.05?,and the change of pH showed the opposite phenomenon.Inorganic carbon utilization model of G.chouae in seawater acidification showed that G.chouae prefers to use CO₂ in seawater acidification,and ocean acidification helped to improve the photosynthetic efficiency of G.chouae.4.Effects of different carbonate system on inorganic carbon uptake of G.chouae.We investigated DIC utilization of G.chouae in different seawater alkalinity?530,1200,1500,1700,1830 and 2450 ?mol·kg-1SW?and different pH?7.6 and 8.1?.The results showed that,pH compensation point,photosynthetic rate and DIC utilization of G.chouae increased significantly with the increasing of seawater alkalinity?P<0.05?.DIC utilization and pH compensation point of G.chouae wavelike rose with the increasing of concerntrations of CO₂ and HCO3-.The increased proportion of CO₂ influenced the photosynthesis of G.chouae,which confirmed the conclusions by experiment two.5.Effects of Hg²⁺ and Pb²⁺ on the growth and photosynthetic physiological characteristics of G.chouae.We investigated the impact of Hg²⁺and Pb²⁺ on the growth and photosynthetic physiological characteristics of G.chouae by exposing algal thalli to five concentrations of HgCl2 and PbCl2,the reference group was in seawater without Hg²⁺ and Pb²⁺.The growth rate,photosynthetic rate,pigment contents,chlorophy? fluorescence characteristics and the activities of RuBisCO and PPDK in the thalli were measured after seven-day incubation.The results showed that the special growth rate?SGR?reduced significantly with the increased Hg²⁺ level?P<0.05?,mortality was found at the highest level of Hg²⁺,and the photosynthetic rate declined by 35.48⁷7.50%.Similar trends were also observed for Chlorophyll a?Chla?and Carotenoid?Car??P<0.05?.The Phycoerythrin?PE?and Phycocyanin?PC?content decreased significantly after Hg²⁺ level exceed 0.1 mg·L-1?P<0.05?.The variation trend of Fv/Fm and Y???along with the Hg²⁺ concentration was close to a bimodal curve,and the second peak appeared at 0.05 mg·L-1 and the activity of PPDK showed the similar trend.The specific growth rate,Chla and Car decreased significantly after Pb²⁺ level reached 1 mg·L-1?P<0.05?.However,no significant change in the level of chlorophy? fluorescence characteristics,as well as PC content,was found among different Pb²⁺ levels.Significantly reduced RuBisCO activity was found at the highest Pb²⁺ level,while PPDK activity increased significantly?P<0.05?.In conclusion,Hg²⁺ and Pb²⁺ both showed detrimental effect on the growth and photosynthesis of G.chouae,however,the algae is more susceptible to Hg²⁺.Stress response was observed after Hg²⁺ level reached 0.01 mg·L-1 and aggravated with increased Hg²⁺ while no stress response was found before Pb²⁺ exceed 1 mg·L-1.