Study On The Photosynthetic Responses To Different Densities Conditionsinmarine Macroalgae

Growth density is the critical environmental factor affecting physiological and biochemical traits of marine macroalgae.The responses of marine macroalgae to growth densitymay vary with various environmental factors under which the marine macroalgae were grown.This study adopted four species of marine macroalgae: Porphyra haitanensis?Bangiales,Rhodophyta?,Gracilaria lemaneiformis?Gigartinales,Rhodophyta?,Ulva conglobata?Ulva,Chlorophyta?and Sargassum horueri?Turner?C.Agardh?Phaeophyta?as experimental materials.They were cultured under outdoor conditions.The treatments were designated as three levels of growth density,in order to examine the effects of growth density on physiological and biochemical traitsin marine macroalgae grown at different levels ofCO₂,temperature and/or pH.The main results were as follows:1.The thallus of P.Haitanensis were cultured under different levels of density(1 g·L^-1,2 g·L^-1,4 g·L^-1)and CO₂concentrations(390,800?L·L^-1),aming to study their effects on growth,chlorophyll fluorescence and pigment contents.To truely simulate the natural environment,this experiment was carried out in outdoor.The results showed thatelevated CO₂ concentration significantly improved the growth of P.Haitanensis,and this kind of improvement under lower cultural density is more significant.Compared to low and medium cultural density(1 g·L^-1,2 g·L^-1),the content of chlorophyll-??Chl??and carotenoid?Car?significantly increased with high cultural density(4 g·L^-1),but it was unaffected by the elevated CO₂ concentration.Neither the content of phycobiliproteins?PB??including phycoerythrin,PEandphycocyanin,PC?nor the content ofsoluble-protein?SP?exhibitedsignificant change under different levels of cultural densitiesor elevated CO₂ concentration.Similarly,effects of elevated CO₂ on apparent photosynthetic efficiency???,maximum relative electron transport rate?rETRmax?and optimal photochemical yield ofphotosystem??PSII??Fv/Fm?were not notable.However,under high cultural density of 4 g·L^-1,values of?,r ETRmaxand Fv/Fmwere significantly increased.2.G.lemaneiformisand U.conglobatawere cultured under different levels of density(1 g·L^-1,2 g·L^-1,4 g·L^-1)and CO₂concentrations(390,800?L·L^-1),aming to study the effects of growth densities on photosynthesis of this two macroalgae under different CO₂ levels.The results indicated that the photosynthetic responses to growth densities are different between G.lemaneiformis and U.conglobata.The values of Pmax?a and Rdin G.lemaneiformisincreased as the growth densities increasing,but these values inU.conglobata decreased.Under the two CO₂ concentration levels,the responses ofPmax?a and Rd in the two macroalgae to growth densities wereenhanced under low density condition,and this kind of response will be affected by elevated CO₂ concentration.Elevated CO₂ decreased the positive effect on Pmax,a andRdof G.lemaneiformis and negative effect of U.conglobatafor increasing growth densities.3.The influences of growth densities on photosynthesisof U.conglobata under different temperature and pH levels were studied.The results showed that,the Pmax?a and Rdof U.conglobataincreased as temperature rising from 20? to 25?.Teperature rising from25? to 30? also increased Rd,but had no influences onPmax,a.Under high density(12 g·L^-1)and low pH value?7.8?,Ik significantly increased while temperature rising from 25? to 30?.High pH value decreased the Pmax?a of U.conglobata.The Pmax?a of U.conglobata significantly decreased while growthdensity rising,but Ik increased;This decreasings of Pmax?a and Rdwere more obvious when the growth densities increasing from low density to medium density.Lower pH value?7.8?and temperature?20??depressed the response of Pmax and ain U.conglobatato growth densities,and lower temperature?20??also depressed the response of U.conglobata?sRd.4.The physiological responses in representative intertidal seaweeds with contrasting location distributions under different growth densitieswere explored in the present research.Sample ofS.horneri was collected from high,middle and low intertidal zone.The results showed that the contents of Chl a andCar,Pmax and IkofS.horneri grown at low tidal zone were depressed.The relative uppertidal zone provided favorable condition for elevating photosynthesis performance of S.horneri.Moreover,as the population density increasing,the algalPmax,?andRd increased,but the Ikreduced.These indicated that low population density can improve population photosynthetic performance of S.horneri.The effect of increasing population density on photosynthesis performance of S.horneri was affected by representative tidal zone.The changes of Pmaxin S.horueri in population level responsed to growth densities under middle intertidal zone is the most significant,as well as changes of ?and Ikat high tidal zone.In conclusion,the responses of seaweeds to growth densities were depended not only on specific-species,but also on the growth conditions such asCO₂ concentrations,temperature and pH levels.High growth density in the culture decreased RGRof P.haitanensis,anddepressed the photosynthesis of P.Haitanensis and U.conglobata,while the photosynthesis of G.lemaneiformis was enhanced.The photosynthesis in population level of U.conglobata and S.horueri were depressed by higher growth densities.Low pH?7.8?and temperature?20??depressed the negative response of photosynthesis of U.conglobata and S.horueri to different growth densities in population level.The photosynthetic changes in population level ofS.horueridue to growth densities were enhanced at low intertidal.The research provides basic data for proper cultivation and life function response characteristic of macroalgae under thebackground of marine environmental change.