Study On The Responses Of Photosynthetic Function To Changing Carbonate System In Three Farmed Marine Macroalgae

Ocean carbonate system drives photosynthesis of marine macroalgae,and thereby,the carbonate system is important environmental factor affecting macroalgal growth and their physiological and biochemical metabolisms.This study adopted three maricultural macroalgae,Gracilaria lemaneiformis,Porphyra haitanensis,and Hizikia fusiformis as experimental materials,aiming to examine the effects of changing carbonate system conditions on their dark respiration(Rd)and net photosynthetic rate(Pn),and to investigate how such responses are affected by light-temperature conditions.Furthermore,the macroalgae were cultured in six kinds of carbon system conditions for a week,in order to examine the effects of growth and photosynthetic activity to changing total inorganic carbon(TIC)and pH.The main results were as follows:1.The treatments were controlled including two TIC levels(ambient-TIC,AC;enriched-TIC,EC),two light(limited-light,LL;saturated-light,SL),four pH levels(7.7,8.1,8.9,9.3),and four temperature conditions(16°C,19°C,22°C,25°C),in order to explore the short-term responses of Rd and Pn in G.lemaneiformis and P.haitanensis to those different environmetal conditions.The results showed that temperature was the most important factor affecting Rd of both red algae,and higher temperature enhenced Rd significantly,while there were no significant differences of Rd among different carbonate systems conditions.Light was the primary factor affecting Pn,and limited-light significantly inhibited the Pn of both red algae.Carbonate system was the secondary factors affecting Pn of both red algae,while the response to temperature of Pn were affected by light conditions and TIC levels.Photosynthetic carbon limitation of both red algae were about 10% under ambient carbonate system in seawater,but the limitation degrees were increased with increasing pH.Elevated-TIC concentration can alleviate the inhibition of high pH.Carbonate system was the first factor affecting photosynthetic carbon limitation of two algae,and TIC level played more important role in carbon limitation than pH did.Both Rd and Pn of P.haitanensis were higher than those of G.lemaneiformis,while Rd/Pg of P.haitanensis is lower than that of G.lemaneiformis.Those results indicated that the metabolic activity and biomass accumulation rate of P.haitanensis were significantly higher than G.lemaneiformis.2.The treatments were designed as two TIC levels(AC and EC),and three pH levels(8.2,9.0,9.4),in order to examine the effects of elevated-TIC and high pH on growth and biochemical activity of G.lemaneiformis grown under six kinds of carbonate systems.The results shown that increased pH has no significantly effect on photosynthetic pigments content(Chl a,Car,PE and PC)of G.lemaneiformis,but high pH significantly reduced the photosynthesis and growth.The negative effect of high pH on G.lemaneiformis could be alleviated by enriched-TIC.Meanwhile,Enriched-TIC significantly reduced photosynthetic pigments content and maximum relative electron transport rate(rETRm).The capacity to extract HCO3-in seawater remained unchanged with the changing growth conditions.We proposed that increasing atmospheric CO2 would be conducive to the aquaculture of G.lemaneiformis through the decline of pH and coinstantaneous increase of TIC in seawater.3.The treatments were designed as two TIC levels(AC and EC),and three pH levels(8.0 8.6,9.2),in order to examine the effects of elevated-TIC and high pH on growth and biochemical activity of young H.fusiformis grown under six kinds of carbonate systems.The results displayed that increased pH significantly reduced the photosynthesis and growth of young H.fusiformis by decreasing TIC and NO3-uptake rates,rETRm,apparent photosynthetic efficiency(?)and optimal photochemical yield(Fv/Fm).However,the negative effect of high pH on growth and photosynthesis could alleviate by enriched-TIC.relative growth rate(RGR)of young H.fusiformis were unchanged,while the TIC uptake rate increased with increasing TIC concentration under normal pH(8.0).In conclusion,short-term responses of Rd and Pn of G.lemaneiformis and P.haitanensis to changing carbonate system conditions were depended on light and temperature conditions.Change of temperature in short-term was the primary factor that affecting Rd,while light intensitiy was the most important fator affecting Pn for both red macroalgae.When exposured to different carbonate system conditions in short-term,Rd of two macroalgae were unchanged,while Pn were more affected by TIC concentrations than pH levels.Similarly,photosynthetic activity and RGR of G.lemaneiformis and young H.fusiformis were severly inhibited by high pH with ambient TIC.Enriched-TIC alleviated the inhibitation of high pH on RGR.The biochemical activity and RGR of the two macroalgae exhibited no significant differences between the two TIC concentrations with normal pH in seawater.We proposed that reducing culture density and/or rising atmospheric CO2 would be conducive to the aquaculture of G.lemaneiformis,P.haitanensis and H.fusiformis.