Research On Suitable Conditions And Methods Of Key Links In The Cultivation And Transplanting Of Zostera Marina L. Seedlings

Seagrass,as an important member of the marine ecosystem,has a very important ecological function in the dense formation of seagrass beds in the marine ecosystem.Affected by natural factors and human activities,the global seagrass beds are experiencing large-scale degradation.There are many methods for transplanting and repairing seagrass beds,among which cultivating seeds into seedlings as transplant donors under controllable conditions is one of the practical and effective methods.Although significant progress has been made in the development of technology for seedling cultivation,further exploration is needed to determine appropriate conditions and methods for rational substrate ratios and amounts,efficient seed storage,and increased survival rates after seedling transplantation.This study focused on Zostera marina L.,a dominant species of seagrass in the northern temperate coastal regions of China.The effects of different sediment-to-substrate ratios(by weight)on Zostera marina seed germination,seedling growth,and light stress resistance were investigated.Based on this experiment,the effect of substrate dosage on the survival and growth of Zostera marina seedlings under the same sediment-to-substrate ratio was determined.The effects of drying,freezing,and vitrification methods for ultra-low temperature preservation of Zostera marina seeds was also evaluated.Additionally,the potential benefits of concurrent cultivation of appropriate quantities of Crassostrea gigas during Zostera marina seedling transplantation were explored and assessed.The main conclusions of this study are as follows:(1)The seedling emergence rate,plant height,and below-ground biomass of Zostera marina were significantly higher in the substrate with a sediment-to-substrate ratio of 3:1 than those in substrates with sediment-to-substrate ratios of 1:1,2:1,and in the in situ substrate treatment group(P<0.05).Zostera marina grown in the substrate with a sedimentto-substrate ratio of 3:1 had the widest leaves,longest roots,largest root diameter,and highest above-ground biomass.Under weak light stress,the chlorophyll fluorescence parameters Fv/Fm and qP of Zostera marina seedlings grown in the 3:1 sediment-to-substrate ratio were significantly higher than those of the other three treatment groups,while NPQ was significantly lower(P<0.05).(2)Under the same substrate-sand ratio,there was no significant difference in germination rate of Zostera marina seeds among different substrate amounts(P>0.05).The substrate amount of 10 g/seed treatment group showed higher seedling emergence rate and main morphological parameters of Zostera marina compared to other treatment groups.However,the carbon and nitrogen element content of Zostera marina seedlings’ leaves in the 10 g/seed treatment group decreased compared to other treatment groups.(3)Effects of cryopreservation on seed germination of Zostera marina.The experimental results show that silica gel dehydration can rapidly reduce the moisture content of Zostera marina seeds,accompanied by a rapid decrease in seed germination rate.The dehydration effect of vitrified dehydration solution PVS2 on Zostera marina seeds was not good,and the germination of Zostera marina seeds was affected with the extension of soaking time.After the Zostera marina seeds were stored at ultra-low temperatures by drying and freezing and vitrification,the seed germination rate was low,and they failed to grow seedlings during subsequent cultivation.(4)The average survival rate of Zostera marina seedlings in the experimental group after 5 months of colonization was 62.7%,which was significantly higher than that of the control group(P<0.05).The leaf area,root diameter,root volume and abovegroundbelowground biomass of Zostera marina in the experiment group were significantly higher than those in the control group(P<0.05),which was 1.27～1.73 times.The presence of Crassostrea gigas significantly increased the plant height,leaf width,root length,and primary productivity of seedlings(P<0.05),while reducing leaf epiphyte biomass(P<0.05).The research results provide new ideas and data support for improving the efficiency of the colonization stage of artificially cultivated seedlings and optimizing the restoration method of Zostera marina resources based on artificially cultivated seedlings.