Inhibition Effect And Mechanism Of Ulva Prolifera Extracts On Early Growth Of Spartina Alterniflora

Spartina alterniflora（S.alterniflora）,a highly invasive plant,has caused a serious threat to ecosystem biodiversity and economic development in coastal areas of many countries.As S.alterniflora grows in coastal beach,it is difficult to carry out mechanical construction.In addition,due to the well-developed root system,strong stress resistance,fast recovery and other factors of S.alterniflora,the existing control methods have a lot of disadvantages,such as high cost and slow effect.In addition,it is difficult to completely remove S.alterniflora in a short time,and easy to cause environmental pollution and secondary invasion.Biological control,especially the allelopathy inhibition of plants,provides a new idea for controlling the invasion of S.alterniflora as an environmental and effective method.Previous studies have proved that Ulva prolifera（U.prolifera）could secrete allelochemicals to inhibit other species.The use of U.prolifera to control S.alterniflora can not only control the spread of S.alterniflora,but also realize the resource utilization of U.prolifera.In this paper,the allelopathic effects and inhibition mechanism of U.prolifera extracts on the seed germination and seedling growth of S.alterniflora were studied by laboratory control experiment.The sustained-release agent was prepared by embedding U.prolifera extract with polyvinyl alcohol（PVA）/sodium alginate（SA）hydrogel,and its inhibition effects on seedling growth of S.alterniflora were explored in constructed wetland reactors.The main research results are as follows:（1）Effects of U.prolifera extract on seed germination and seedling physiological indexes of S.alternifloraThree different treatments（aqueous,methanol and ethyl acetate extracts）could inhibit the seed germination and seedling growth of S.alterniflora by reducing the germination percentage and germination index of seeds,decreasing the seedling length and root length of seedlings.At the same time,U.prolifera extract would affect the activities of superoxide dismutase（SOD）,catalase（CAT）and peroxidase（POD）and the contents of malondialdehyde（MDA）and proline（Pro）,resulting in the destruction of the antioxidant system and cell osmotic balance of S.alterniflora.The higher the concentration of extract,the higher the inhibition effect.Among them,the aqueous extract of U.prolifera had the best inhibitory effect on S.alterniflora.When the concentration of aqueous extract reached0.20 g·m L^-1,the germination percentage of S.alterniflora decreased to 49.53%of the control,the fresh weight and dry weight of seedlings decreased by 13.73%and 9.53%respectively,the activities of SOD and CAT decreased by 74.74%and 45.49%respectively,and the root activity decreased by 80.58%.（2）Analysis of differentially expressed genes（DEGs）of S.alterniflora after adding U.prolifera extractIn order to study the changes of S.alterniflora at the gene level after adding U.prolifera extract,transcriptome sequencing results were analyzed.The results showed that the transcription factors of S.alterniflora were enriched in MYB superfamily,AP2/ERF,C2C2,NAC and other families after adding U.prolifera extract.The expression of genes related to amino acid metabolism and photosynthesis were upregulated,while the expression of genes related to energy generation and metabolism were downregulated.The DEGs are enriched in“ribosomes”,“carbon fixation in photosynthetic organisms”,“photosynthetic antenna proteins”and other pathways.The results showed that the stress of U.prolifera extract affected the normal physiological function of S.alterniflora.（3）Analysis of allelochemicals in U.prolifera extractThe components of U.prolifera extract were analyzed by GC-MS.It was found that the extract was rich in organic acids,alcohols and esters that could inhibit the growth of plants.Among them,Valine could inhibit the growth of other algae and phytoplankton,resulting in the obstacle of continuous cropping of plants;Butanoic acid,butyl ester and Hexanedioic acid,bis（2-ethylhexyl）ester could lead to the excessive accumulation of reactive oxyradical and the decrease of chlorophyll a,and finally lead to cell death of plant.Therefore,the above substances measured in U.prolifera extract could be the main allelochemicals that inhibit the growth and reduce the plant biomass of S.alterniflora.（4）Effects of PVA/SA hydrogel sustained-release agent on the growth of S.alternifloraIn order to facilitate the practical application,PVA/SA hydrogel was used to embed U,prolifera extract and prepare sustained-release agent.After addition,the biomass and photosynthesis of S.alterniflora in the reactor were affected to varying degrees.The results showed that with the increase of salinity,the survival rate,fresh weight and chlorophyll b content of S.alterniflora first decreased,then increased and then decreased rapidly,while the dry weight and chlorophyll a content of seedlings increased first and then decreased.When the salinity increased to 30 ppt,the content of chlorophyll and the proportion of dry weight of S.alterniflora decreased rapidly,and the survival rate was only 21.67%.The results showed that the sustained-release agent prepared by U.prolifera could inhibit the growth of S.alterniflora,which provided a feasible method for controlling the invasion of S.alterniflora and realizing the resource utilization of U.prolifera.