Interspecies Competition Between Three Typical Marine Diatoms And Chattonella Marina And Scrippsiella Trochoidea

Growth and interspecies competition were studied between three typical marine diatoms(Chaetoceros curvisetus,Phaeodactylum tricornutum,and Skeletonema costatum),Chattonella marina and Scrippsiella trochoidea under different nutrient conditions and initial cell densities using mono-cultures and co-cultures.The effects of cell-free filtration and cell disruption of three diatoms on the growth of S.trochoidea were studied to investigate the allelopathic competition between the diatoms and the dinoflagellates.GC-MS technique was used to analyze the volatile metabolites in cell disruption of three diatoms qualitatively and semi-quantitatively,and the composition of polyunsaturated aldehydes in the secondary metabolites of diatoms was discussed.In addition,the effects and toxicity of typical polyunsaturated aldehydes,decadienal,on the growth of S.trochoidea and the three diatoms were studied.The results of the study discussed the growth and interspecific competition effect between the typical marine phytoplankton,and investigated the toxicity of decadienal the typical marine phytoplankton taxa.The research results may provide some scientific basis for prevention of algal blooms,and thus protect the marine environment.The main results are as followings:(1)In mono-cultures,the growth of all of the five microalgal species,C.curvisetus,P.tricornutum,S.costatum,C.marina and S.trochoidea deplaced a shorter lag phase and entered into the logarithmic growth stage and stationary stage earlier as the increasing of the initial cell density.The maximum cell densities were not influenced by the initial cell density.However,the growth of algal cells was significantly influenced by nutrient limitation,and the maximum cell densities were less than one half of those in f/2 enriched medium.The results suggested that nutrient limitation did not benefit the growth of the marine microalgae,and nutrient concentrations determined the maximum density of the algal cells.(2)The three diatoms,C.curvisetus,P.tricornutum,and S.costatum,inhibited the growth of C.marina and S.trochoidea significantly in co-culures in f/2 medium.Cell densities of C.marina and S.trochoidea decreased gradually,and finally all cells dead in the co-cultures.In nutrition limitation co-cultures,the growth of C.marina and S.trochoidea was significantly inhibited by diatoms as well,but remained certain cell densities.Though the growth of diatoms was significantly inhibited by C.marina and S.trochoidea in co-cultrues,the cell densities of the three diaotms were much higher than those of C.marina and S.trochoidea.Results suggested diatoms take more advantages in the interspecific competition with the other microalgae species in both nutrient enrichment and limitation conditions.(3)The growth of S.trochoidea was inhibited by the cell-free filtrations and cell disruptions of the three diatoms,and the inhibitory effects of C.curvisetus and P.tricornutum were stronger than that of S.costatum.Furthermore,cell disruptions of diatoms were more efficient to inhibit the growth of S.trochoidea.The results suggested that diatoms produced inhibitory effects on the growth of S.trochoidea by allelopathy.(4)Components of volatile metabolites in the cell disruptions of the three diatoms were analyzed by GC-MS.A total of 46 compounds were detected from the cell disruption of C.curvisetus,among which high proportion of aldehydes were detected accounting for 43.22% of the total volatile metabolite compounds.One hundred and seventeen compounds were detected from S.costatum,among which hydrocarbons were the most abundant.Sixty-six compounds were analyzed from P.tricornutum.Generally,the composition and content of volatile metabolites were different among the three diatoms.(5)There were 14 volatile aldehydes produced by the three diatoms.A total of 7 aldehydes were detected from C.curvisetus,contributing 43.22% of the total volatile metabolites.Nine aldehydes were analyzed from S.costatum with the relative proportion of 8.82%.Six aldehydes were detected from P.tricornutum,accounting for 6.48% of the total volatile compounds.The dominant aldehyde in C.curvisetus was phenylglyoxal,and were decadienal and methylcyclopentenal for P.tricornutum,and acetaldehyde,octadienal and heptadienal for S.Costatum.Meanwhile,four aldehydes hexanal,heptadienal,?-cyclocitral and decadienal,were detected in all of the three diatoms,in which decadienal and heptadienal were relatively higher in C.curvisetus.(6)Decadienal affected the growth,chlorophyll content and Fv/Fm values of C.curvisetus,P.tricornutum,S.costatum and S.trochoidea.S.trochoidea was more sensitive to decadienal than the three diatoms,and 1 mg/L decadienal showed significantly inhibitory effects on the growth of S.trochoidea.While the significantly inhibitory concentrations for diatoms were > 2 mg/L.The 96 h EC50 values of decadienal on the growth of C.curvisetus,P.tricornutum,S.costatum and S.trochoidea were 2.46 mg/L,3.27 mg/L,2.67 mg/L and 3.78 mg/L,respectively,all of which belonged to the highly toxic level.The Fv/Fm values of the all four microalgae decreased significantly under the stress of different concentrations of decadienal,and the inhibition increased as the increasing of dose and exposure time.The results suggested that decadienal could inhibit the growth of microalgae through the photosynthesis system.