A Study On The Ecological Adaptability Of Sporophytes In Costaria Costata

Based on the economic and ecological value of large economic seaweed,the development of new cultivated species with potential is the guarantee for the healthy and diversified development of seaweed cultivation industry.Costaria costata is a large brown alga with high nutritional value and economic value,but it is not an indigenous species in China.In this study,MaxEnt model and ArcGIS were used to predict the suitable distribution and potential invasion risk of C.costata in China,and the effects of different environmental factors on sporophyte growth,photosynthesis,basic nutrients and antioxidant physiological responses of C.costata were explored to provide a theoretical basis for the introduction and cultivation of C.costata.Main study results are as follows:（1）the model prediction performance was the best when the model running parameter regularization parameter was 1 and the ratio of training set to test set was70:30.A total of eight variables,namely,minimum light intensity,mean annual light intensity change range,mean annual phosphate,mean annual phosphate change range,minimum monthly mean salinity,mean annual salinity change range,minimum monthly mean temperature and mean annual temperature change range,were selected for the construction of the suitable prediction model of C.costata,with temperature and light intensity having the greatest effect on the natural distribution of C.costata.The suitable areas of C.costata in China are mainly distributed in the Yellow Sea and Bohai Sea,accounting for about 11.32%of the area,of which 8.08%are marginal suitable areas and low suitable areas,and medium suitable areas and high suitable areas account for 1.33%and 1.91%,respectively,mainly located in Liaodong Bay,of which Liaodong Bay,Dalian and the coast of Shandong Peninsula are suitable areas for the introduction and aquaculture of C.costata,but some areas of Liaodong Bay indicate high invasion risk,and if artificial cultivation is carried out,the evaluation of ecological safety should be strengthened.（2）The suitable range for the growth of young sporophyte of C.costata is 6-18℃,preferably 10℃;while at 22℃,the algae decayed and decayed in large areas and showed negative growth.Algal body F_v/F_mwas not significantly different in the range of 6-22℃.During the culture cycle,both P_tand P_nmaxwere higher at 6-14℃,especially at 10℃in the late culture period（5 days）;at 6℃,R_dwas highest on the 3rd day of culture;while at 22℃,algal R_dincreased significantly with culture time.Compared with the 10-18℃group,the specific activities of SOD,CAT,and ASAFR in young sporophyte basically did not increase or decrease significantly at 22℃,but the activity of APX was higher than that of the 6℃,14℃,and 18℃groups,especially the contents of Fucox,Car,and soluble proteins were second only to the 14℃group in all temperature groups.At 6℃,MDA and H₂O₂contents were also higher than those in the 10-18℃group,while the specific activities of SOD and ASAFR were also the highest.Temperature positively regulates ash,carbohydrate and crude fiber content in young sporophyte of C.costata.（3）In the range of 30-120μmol/（m²·s）,the RGR was the largest at 60μmol/（m²·s）,and in the range of 90-120μmol/（m²·s）,a small area of albinism and perforation appeared in the slight part of young sporophyte of C.costata.At 60μmol/（m²·s）,F_v/F_mwas higher than other groups,while F_v/F_mshowed a decreasing trend in other groups overall.Both P_tand P_nmaxincreased with the increase of light intensity,and were highest at 60μmol/（m²·s）in the late stage of culture;however,the R_dof C.costata in the 60μmol/（m²·s）group was significantly lower than that in the other light intensity groups with the extension of culture time.Chl a,Foux and Car contents were higher at 30-60μmol/（m²·s）.Compared with 60μmol/（m²·s）group,the contents of H₂O₂,MDA and the specific activity of CAT in algae of high light group（90-120μmol/（m²·s））were not significantly different,but the specific activities of ASAFR,SOD and APX were significantly decreased,and the soluble protein was significantly increased;the contents of H₂O₂,the specific activities of ASAFR,SOD,CAT and APX in C.costata of low light group（30μmol/（m²·s））showed a downward trend,in which the contents of H₂O₂and the specific activity of CAT were significantly decreased.Light intensity positively regulates crude protein and fat content in young sporophyte of C.costata,while carbohydrate content is negatively correlated with light intensity.（4）Young sporophyte of C.costata have a wide salinity tolerance and can grow at salinities 26-36,with RGR being greatest at salinities 36,while they grow slowly at salinities 21 and the algae are severely decaying.At 5 days of culture,F_v/F_mincreased in 36 groups of salinity 21,especially in 36 groups;at 7 days of culture,F_v/F_mrecovered significantly in 26-36 groups of salinity and was higher than that in the control group,while F_v/F_mremained at a lower value in the low salt group（21）.With the extension of culture time,P_tand P_nmaxin salinity 36 group increased significantly to the highest value,which was significantly higher than that in salinity 21 group;at the early stage of the experiment（1d）,algal R_dwas at a higher level at low salt（21）and high salt（36）,but with the extension of culture time,relative to salinity 21-26,R_dwas at a lower level in salinity 31-36 group.Chl a,Foux,and Car of C.costata bodies did not change significantly in the salinity range 26-36,while they showed a decreasing trend at low salinity（21）.MDA content decreased significantly at salinity 26-31,and there was no significant difference in soluble protein content,ASAFR specific activity,and SOD specific activity among different salinity groups,and both CAT and APX were lowest at salinity 31,with CAT specific activity significantly higher in salinity 21 group than in salinity 31 group,while APX specific activity significantly higher in salinity 36 group than in salinity 26 and 31 groups.At low salt stress,C.costata accumulate crude protein,while at high salt,they accumulate large amounts of carbohydrates.（5）Compared with the control group（without N/P）,the growth rate and physiological activity of young sporophyte of C.costata were higher under different nutrient levels of N/P(0.5/0.05 mg·L^-1),N/P(1/0.1 mg·L^-1),and N/P(2/0.2 mg·L^-1),and the RGR was the highest under N/P(1/0.1 mg·L^-1).After 7 days of culture,F_v/F_min the low control group and N/P(0.5/0.05 mg·L^-1))was significantly lower than that in the high N/P group(N/P(1/0.1 mg·L^-1)and N/P(2/0.2 mg·L^-1)).At high N/P,the algal P_tand P_nmaxwere significantly higher than those in the low N/P group;R_dwas significantly increased in the N/P(2/0.2 mg·L^-1)group on the 10th day,while P_tand P_nmaxwere decreased and R_dwas at a higher level in the low N/P group.The contents of Chl a,Foux and Car in the high N/P group were significantly higher than those in the low N/P group,and the contents of Chl a in the N/P(2/0.2 mg·L^-1)group were the highest,while the contents of Foux and Car in the N/P(1/0.1 mg·L^-1)group were the highest.The contents of H₂O₂,MDA and soluble protein were significantly increased in N/P(2/0.2 mg·L^-1)and control groups,the specific activity of ASAFR was significantly decreased in N/P(2/0.2 mg·L^-1)group,the specific activity of CAT was significantly increased in control group,and the specific activity of APX was significantly increased in control and N/P(1/0.1 mg·L^-1)groups.In the experimental range,the uptake rate of N and P by algae increased significantly with the increase of N/P concentration,but the uptake of N by algae was supersaturated at the level of N/P(2/0.2 mg·L^-1).The crude fiber,crude protein and ash content of young sporophyte of C.costata were positively correlated with N/P concentration,while the carbohydrate content was negatively correlated.