Inhibitory Effect Of Salvinia Natans(L.)all.on Algae And Its Tolerance To The Stress Of Eutrophication

As the eutrophication increasingly deteriorates and algae blooms outbreaks more and more frequently, the global environment of water is becoming worse and worse. The use of higher hydrophytes for eutrophication water governance and harmful algae control has become the research hotspot gradually in the domestic as well as international environmental area.In order to find a kind of higher aquatic plants that can not only effectively restain the growth of algal by secreting allelochemicals, but also be able to bear the stress of eutrophic waters. This study was planned to systematically explore the tolerance of floating plants Salvinia natans(L.)All.to rich nutrient salt, the removal effect of N, P and the inhibiting effect to Microcystis aeruginosa, as well as the inhibiting mechanism on algal. It also comparatively researched the allelopathic interactions between different biomass Salvinia natans(L.)All. and various density Microcystis aeruginosa in co-culture conditions, meanwhile we made the allelochemicals isolated from Salvinia natans(L.)All. and identified them. The obtained results are as follows:1. The tolerance of Salvinia natans(L.)All.to rich nutrient salt and the removal effect of total phosphorus and ammonia nitrogen. The results showed that Salvinia natans(L.)All has strong tolerance to rich nutrient salt, its growth rate of fresh weight increases with the increase of salt concentration, then with the increase of salt concentration it becomes smaller gradually; under perfect condition, the growth rate up to 590.6%. Salvinia natans(L.)All owns powerful capacity to eliminate the phosphorus and ammonia nitrogen existing in waters, the removal rate increases along with the concentration of nutrient salt; the removal rate of ammonia nitrogen reached the maximum up to 87.06% in 0.5 x Hoagland solution, while the phosphorus maximum removal rate reach the highest-77.87% in 0.25 x Hoagland solution.2. The allelopathic interaction effect between Salvinia natans(L.)All and Microcystis aeruginosa. The results of the study show that: The cultured water of Salvinia natans(L.)All was able to inhibit the growth of Microcystis aeruginosa, higher concentration of aquaculture water would induce more intensive algicidal effect and the greater inhibitory rate. Under co-culture conditions, different amounts of Salvinia natans(L.)All owns killing effect of diverse degree to Microcystis aeruginosa, the more Salvinia natans(L.)All planted, the increasing severe damage to algal cells; under the same conditions, low density of Microcystis aeruginosa promoting growth of leaves pairs and body length, increase the fresh weight and chlorophyll content of Salvinia natans(L.)All; however, high density of Microcystis aeruginosa inhibited the growth of Salvinia natans(L.)All, decreased the content of chlorophyll a, chlorophyll b, and total chlorophyll; There is a lowpromoting high-suppression relationship between Salvinia natans(L.)All and Microcystis aeruginosa.3. The algicidal mechanism research of Salvinia natans(L.)All. The results showed that: the extracted fluid of Salvinia natans(L.)All could significantly inhibit the growth of Microcystis aeruginosa., the higher concentration of extracted fluid and the longer treated time, the survival biomass of algal is less, the mortality of cell is higher. During this period, leaching liquor of Salvinia natans(L.)All also caused the conductivity of algae fluid increase, the content of dissolvable nucleic acid and protein in microalgae suspension rise; the CAT, POD, SOD activity of cell antioxidant enzymes, as well as the polysaccharide content of intracellular and extracellular were all present when a first went up then rapid downtrend.4. Separation and identification the allelochemicals isolated from Salvinia natans(L.)All. The results showed that: From the crude extract of Salvinia natans(L.)All algicidal experiments, we can see the algicidal effect as follows: ethyl acetate extract > acetone crude extract > ethanol crude extract > water crude extract. Let the ethyl acetate extract and acetone crude extract purified by macroporous resin that is because they both own better inhibiting effect to Microcystis aeruginosa., and then through gas chromatography-mass spectrometry(GC-MS) analysis, preparation by screening, conjecture diacetone alcohol, methyl isobutenyl ketone, 5-methyl-2-(1-methylethyl)-1-hexanol, pentadecanal, 14-heptadecenal, cumene, butyl acetate, ascorbyl dipalmitate, dibutyl phthalate, 1,2-benzenedicarboxylic acid, mono(2-ethylhexyl)ester and phthalic acid, butyl undecane ester might be allelopathic inhibitory substances of Salvinia natans(L.)All.In conclusion, because of wide distribution of Salvinia natans(L.)All, it not only grows well in eutrophic waters, but also has extremely strong inhibitory effect on Microcystis aeruginosa. Therefore, it will have a perfect application prospect to using the allelopathy of Salvinia natans(L.)All. for the inhibition of algae growth, and the good removal effect of nitrogen and phosphorus in order to govern eutrophic water and prevent algal bloom.