Response Of Allelopathic Effects Of Corallina Pilulifera On Three Red Tide Microalgae To Enhanced UV-B Radiation

Increasingly serious erosion and destruction of ozonosphere is one of the mostconspicuous phenomena of global changes nowadays.Ozone depleting promoted the doseof UV,especially UV-B,radiation increasing,which could produce serious damage effectto biology.Enhanced UV-B radiation can induce various changes of organism at the levelsof ecosystem,community,population,individuals,cell and molecular and further presentobvious ecological and biological effects.At the same time,with intensifications of coastal water eutrophication,severe outbreaksof harmful algal blooms (HABs) had become marine ecological disasters in the world.Since 1990s,red tides presented the features of"large range,high frequency,multiplespecies"in China,and has an increasing trend.This caused greatly threaten to coastalaquaculture and ecological environment.Using feasibly and effective measures to controlHABs were one of important content about red tides study.Biological method controllingred tides were an ideal approach because of its economic and no pollution,whereas thephysical and chemical methods about controlling HABs had second pollution that theycan't overcome by their self.Using interaction between macroalgae and red tidesmicroalgae were considered to be a new way to prevent and control HABs.The present studies deal with the allelopathic effects of macroalgae Corallina piluliferaon three red tide microalgae (Heterosigama akashiwo,Alexandrium tamarense andSkeletonema costatum),and their responses to enhanced UV-B radiation.The mainobjectives of these studies were to provide evidence for the feasibility of using manymacroalgae to control the growth of red tide microalgae,and present the importantfunction about the effect of enhanced UV-B radiation on marine ecosystem.Results showthat: 1 Sensitivity comparative studies on the response of C.pilulifera and three redtides microalgae to enhanced UV-B radiationThe growth of H.akashiwo was inhibited after UV-B radiation treatment,while UV-Bradiation produced stimulatory effect to A.tamarense and S.costatum at lower dose,andstill exhibited inhibitition effect to these two red tides microalgae at high dose of UV-Bradiation.The median effective dose (ED₅₀) of UV-B radiation to H.akashiwo,A.tamarense and S.costatum were 1.63,2.34 and 2.58 J m^-2 respectively.Thus the sensitiveorder of three species microalgae to UV-B radiation was H.akashiwo＞A.tamarense＞S.costatum.Compared with these red tide microalgae,C.pilulifera presented a strongresistance to UV-B radiation,and the EC₅₀ of UV-B radiation to C.pilulifera was notshowed in the range of experimental doses (96h·EC₅₀＞3.0 J m^-2)2 Studies on the allelopathic effects of C pilulifera on three species of red tidemicroalgaeExperiments were conducted under the same laboratory environmental conditions,including the nutrient,pH,light conditions and effects of bacteria in order to investigate theallelopathic effects of fresh tissue,dry powder,aqueous extracts and culture mediumfiltrate of C pilulifera on the growth of microalgae (H.akashiwo,A.tamarense and S.costatum) were evaluated using coexistence culture systems.The results of coexistenceassay showed that the growth of the three microalgae was strongly inhibited by using freshtissues and dry powder of C pilulifera,and H.akashiwo and S.costatum could be killedcompletely at higher concentration.It indicated that there are allelopathic effects of Cpilulifera on three microalgae.Aqueous extracts of C pilulifera also inhibited the growth of three microalgae,andinhibitory effects were enhanced with increasing concentration.This indicated that thereare allelochemicals in C.pilulifera,which could inhibit the growth of red tides microalgae,and further proved that the allelopathic effects of C.pilulifera on three microalgae were carried out mainly through allelochemicals.The effects of C.pilulifera culture medium filtrate exhibited no apparent inhibitoryeffect under initial filtrate addition and semi-continuous addition,which suggested that thefresh tissue of C.pilulifera can not release or little quantifies of allelochemicals toenvironment.This proved that the way of allelopathic effects of C.pilulifera on threemicroalgae were conducted by direct contacting.Allelopathic effects of the fresh tissue of C.pilulifera on three microalgae from high tolow were:S.costatum＞H.akashiwo＞A.tamarense.The results showed that there weresensitivity differences to some extent in allelopathic effects of C.pilulifera on threemicroalgae.Perhaps it was related to the structure of amphithecia of the species red tidesmicroalgae.3 Response of allelopathic effects of C.pilulifera on H.akashiwo to enhancedUV-B radiationThe allelopathic effects of flesh tissue and dry powder of C.pilulifera on H.akashiwowere changed after UV-B radiation stressing.High dose of UV-B radiation treatment (3.0 Jm^-2) significantly decreased the allelopathic effects of fresh tissue on H.akashiwo,whilelow dose of UV-B radiation treatment (0.9 J m^-2) obviously enhanced the allelopathiceffects of fresh tissue and dry powder of C.pilulifera on H.akashiwo.The allelopathic effects of aqueous extracts of C.pilulifera on H.akashiwo were alsoaltered under UV-B radiation treatment.High dose of UV-B radiation treatment (3.0 J m^-2)significantly decreased the allelopathic effects of aqueous extracts on H.akashiwo,whilelow dose of UV-B radiation treatment (0.9 J m^-2) obviously enhanced the allelopathiceffects of aqueous extracts of C.pilulifera on H.akashiwo.This showed that UV-Bradiation treatment changed allelopathic effects or compound quantity of allelochemicalsfrom tissue of C.pilulifera.Namely,high dose of UV-B radiation treatment (3.0 J m^-2)significantly decreased the allelopathic effects or compound quantity of allelochemicals,and low dose of UV-B radiation treatment (0.9 J m^-2) obviously enhanced the allelopathic effects or compound quantity of allelochemicals that from tissue of C pilulifera.The allelopathic effects of C.pilulifera culture medium filtrate were not changed underinitial filtrate addition and semi-continuous addition after UV-B radiation treatment(p＞0.05).It showed that UV-B radiation did not alter the way of allelopathic effects of C.pilulifera on H.akashiwo,and direct contact among cell-cell was still a main approach toconduct the allelopathic effects.4 Study on growth inhibition effects of H.akashiwo by the extracts of C.piluliferaMethanol extracts of C pilulifera showed the highest growth inhibitory activity on H.akashiwo,and they killed all the cells of H.akashiwo at relatively higher concentrations.The EC₅₀ of methanol extracts of C.pilulifera to H.akashiwo was 0.004 ppt.Growth of H.akashiwo was significantly inhibited by the distilled water extracts of C.pilulifera at relatively higher concentrations,but cells of H.akashiwo were not killedcompletely even at the highest concentration.The other three organic solvent extracts (acetone,aether and chloroform) of C.pilulifera had no apparent effects on H.akashiwo,which suggested that there areallelochemicals in C.pilulifera which could inhibit the growth of H.akashiwo,and thegrowth inhibitory substances from the extracts of C.pilulifera had relatively highpolarities.The methanol extracts of C.pilulifera were partitioned to petroleum ether phase,ethylacetate phase,butanol phase and distilled phase by liquid-liquid fractionation.Thebioassays of the activity of every fraction which were carried out on H.akashiwo,indicatedthat petroleum ether phase and ethyl acetate phase had stronger allelopathic effect on H.akashiwo and its effective concentration was 20 mg L^-1;ethyl acetate phase took the secondplace,and its effective concentration was 35 mg L^-1;butanol phase and distilled waterphase had not obvious algicidal effect on H.akashiwo. 5 Response of the extracts of C.pilulifera inhibited growth of H.akashiwo toenhanced UV-B radiation.Compared with distilled extracts of C.pilulifera,which was untreated by UV-B radiation,the distilled extracts of C.pilulifera presented significant inhibitive effects on H.akashiwoat the group of low dose (0.9 J m^-2) of UV-B radiation treatment (p＜0.05);while thedistilled extracts of C.pilulifera promoted the growth of H.akashiwo obviously (p＜0.05)at the group of high dose (3.0 J m^-2) of UV-B radiation treatment.This indicated that boththe groups of low and high dose changed inhibitive effects of the distilled extracts of C.pilulifera on H.akashiwo,and the inhibitive effects were enhanced and weakenedrespectively.Compared with methanol extracts of C.pilulifera,which was untreated by UV-Bradiation,the methanol extracts of C.pilulifera presented significant accelerate effects onH.akashiwo both in the groups of low dose (0.9 J m^-2) and high dose (3.0 J m^-2) of UV-Bradiation treatment (p＜0.05),and promoting effects in the groups of high dose wasstronger significantly than that in the groups of low dose.This indicated that inhibitiveeffects of the methanol extracts of C.pilulifera on H.akashiwo could be changed both inthe groups of low dose and high dose of UV-B radiation treatment,and the inhibitiveeffects were weakened.Extracts of acetone,aether and chloroform from C.pilulifera had not changed thegrowth of H.akashiwo after treatment by UV-B radiation either in high dose group (0.9 Jm^-2) or low dose group (3.0 J m^-2).Allelopathic activity of petroleum ether phase and ethyl acetate phase from themethanol extracts of C.pilulifera could be altered by UV-B radiation treatment,theinhibitive effects of C.pilulifera on H.akashiwo were significantly decreased (p＜0.05).The effects of butanol phase and distilled phase from the methanol extracts of C.piluliferaon H.akashiwo were not changed after UV-B radiation treatment.