The inhibitory effects of Ulva prolifera extracts on early growth of Spartina alterniflora and the underlying mechanisms

Spartina alterniflora, a highly invasive plant, has caused a serious threat to ecosystem biodiversity and economic development in coastal areas of many countries. In this study, the allelopathic effect of Ulva prolifera extracts on seed germination and seedling growth of S. alterniflora was studied. The results showed that three different treatments (water, methanol and ethyl acetate extract) could inhibit the seed germination and seedling growth of S. alterniflora by reducing the germination proportion and germination index of seeds, decreasing the seedling length and root length of seedlings, and affecting the lipid peroxidation and enzyme activity. The higher the concentration of the extracts, the higher the inhibition effect. When the aqueous extract concentration reached 0.20 g/mL, the germination proportion of S. alterniflora decreased to 49.53% of the control. RNA-seq analysis showed that the expression of genes related to amino acid metabolism and photosynthesis were both upregulated, and genes related to energy generation and metabolism were both downregulated after adding the extracts. GC-MS analysis indicated that the U. prolifera extract was rich in organic acids, alcohols and esters, among which butanoic acid, butyl ester, Valine and Hexanedioic acid, bis (2-ethylhexyl) ester might be the dominant allelochemicals. In order to facilitate field dosing, prolong action time and control release effect, PVA/SA hydrogel embedded U. prolifera extract was used to obtain a sustained-release agent. In addition, the survival rate of S. alterniflora was significantly reduced, which was only 21.67% at the salinity of 30 ppt. The results of this study provide a feasible method for controlling the invasion of S. alterniflora and achieving the waste utilization of U. prolifera.