Effects Of Environmental Factors On Growth And Photosynthetic Physiology Of Betaphycus Gelatinus

Betaphycus gelatinus is an important economical macroalgae worldwide which used as raw material in carrageenan industry.B.gelatinus distributed in tropical and subtropical coral reef sea area,including Southeast Asia,Hainan Island,and the Dongsha Islands.The wild resources of B.gelatinus in Hainan declined seriously recently years.The yield of cultivated B.gelatinus increase rapidly in Hainan area.In B.gelatinus cultivation,wild B.gelatinus were used as seed algae in vegetative propagation,which was used as main method.In current cultivation mode,single breeding mode and germplasm resources,combined with long-term vegetative propagation,resulted in the disease outbreak and the decrease of quality in B.gelatinus cultivation Therefore,it is urgent to develop new cultivation mode and germplasm resources.At present,there are few studies on nutrient absorption characteristics and environmental adaptability differences among different B.gelatinus strains.In current study,appropriate nutrient concentration and supply mode of B.gelatinus,B.gelatinus as the research object,through the study of the establishment of low nutrient concentration sustainable culture system of B.gelatinus;The adaptability of green mutants to different environmental factors（temperature,light intensity,light quality and salinity）was studied.Wild type red B.gelatinus was used as a control to analyze its growth advantages,which provided reference for the study of green B.gelatinus mutant.The survey and ecological restoration of seaweed resources in land-based pond culture,Marine culture,Xisha islands and reefs were carried out to explore the wild multiplication mode and ecological restoration ability of B.gelatinus.The main research results are as follows:1.Effects of nutrient concentration and supply mode on B.gelatinusThe specific growth rate of B.gelatinus was significantly higher than other groups at the conditions of N:P=25:1(100μmol·L^-1:4μmol·L^-1)and NO₃^--N:NH₄⁺-N=3:1,which was 2.13±0.32%·d^-1.A kind of the nutrient solution was designed and applicated in indoor cultivation of B.gelatinus.A new macroalgae cultivation mode with constant low nutrient concentration was created and applicated in B.gelatinus cultivation.Several environment factors,including photoperiod,water-air interaction,water flowing and temperature,were also designed in current system,which could fulfill the simulation of marine.At the cultivation mode of constant low nutrient concentration,the specific growth rate,pigment content and photosynthetic parameters of B.gelatinus were significantly higher than that at the mode of supply once.The specific growth rate of B.gelatinus was 1.94±0.25%·d^-1,the content of chlorophyll a was 150.73±17.52μg·g^-1,the content of carotenoid was 44.89±4.9μg·g^-1,and the content of phycoerythrin was 863.03±99.46μg·g^-1 under the constant concentration of 5μmol·L^-1NH₄⁺-N.The phycocyanin content was 339.14±9.01μg·g^-1,allophycocyanin content was 420.82±22.52μg·g^-1,Y（Ⅱ）was 0.167±0.013,rETR was 1.752±0.132,q P was 0.754±0.006,NPQ was 0.606±0.011,and Fv/Fm was0.539±0.011.The study showed that the constant concentration of continuous cultivation can improve the specific growth rate,pigment content and photosynthetic efficiency of B.gelatinus.2.Comparative study on the growth and photosynthesis of different color strains of B.gelatinus.The phycoglobin content of green B.gelatinus(256.11±21.41μg·g^-1)was significantly lower than that of red strain B.gelatinus(451.73±24.89μg·g^-1)（P<0.05）.However,there was no significant difference in other pigment.Therefore,the decrease of phycoerythrin content was the main reason for the green strain B.gelatinus color of algae.It was found that the specific growth rate and photosynthetic parameters of green B.gelatinus were higher than those of red B.gelatinus in the comparison experiment of single factors such as temperature,light intensity and salinity.Under blue light,the adaptability of green s B.gelatinus was weaker than that of red B.gelatinus,and the specific growth rates were 0.21±0.10%·d^-1 and 0.77±0.10%·d^-1,respectively.The Fv/Fm,NPQ,Y（Ⅱ）and rETR of green B.gelatinus were significantly higher than those of red B.gelatinus（P<0.05）,especially at the condition of 30℃and 380μmol·m^-2·s^-1,the specific growth rate of green B.gelatinus(2.76±0.02%·d^-1)was significantly higher than that of red B.gelatinus(2.17±0.01%·d^-1)（P<0.05）.The Fv/Fm of green B.gelatinus（0.57±0.021）was significantly higher than that of red B.gelatinus（0.342±0.021）（P<0.05）,and the rETR of green B.gelatinus（4.66±0.26）was significantly higher than that of red B.gelatinus（3.42±0.021）（P<0.05）.The results showed that green B.gelatinus had more advantages in growth and photosynthetic physiology than red B.gelatinus in high temperature and high light environment(30℃+380μmol·m^-2·s^-1).3.Wild cultivation and breeding of B.gelatinusNew mode of B.gelatinus aquaculture was explored by pond rearing,floating frame breeding and cement frame bottom sowing.The specific growth rate of B.gelatinus decreased significantly with the increase of water depth at the range of 0.6-1.2 m.The specific growth rates in different water depths were 2.16±0.07%·d^-1（0.6m）,1.04±0.08%·d^-1（0.9 m）and 0.57±0.07%·d^-1（1.2 m）.The temperature of different water depths is basically the same,and the light intensity decreases with the increase of water depth,which may be the main reason for the significant decrease of specific growth rate of B.gelatinus.In the marine culture experiment,the specific growth rate of B.gelatinus from November to December was 1.39±0.01%·d^-1,1.31±0.24%·d^-1 and 1.20±0.04%·d^-1.During the experiment,it was found that the light intensity did not change significantly with the passage of time,but the temperature showed an obvious downward trend.The temperature change is one of the main factors restricting the growth of B.gelatinus in Marine culture.B.gelatinus resource restoration was carried out in the Qilian islands of the Xisha Islands.Through the investigation of macroalgae resources in Xisha Islands,50species of reef macroalgae were found,belonging to 3 phyla,15 orders,28 families and 41 genera,with seasonal variations.There is no distribution of B.gelatinus found,the degradation of resources is extremely serious.In area of the Qilian islands,a total of 240 algae were planted at 600 m² of 6 sites.Compared with the unplanted area,algae and marine organisms increased significantly,which can effectively improve the biological diversity in the aquaculture waters.The results of this study provide a reference for indoor and field culture methods,green B.gelatinus research and marine resource restoration.