Study On The Hormesis Induced By Organophosphorus Pesticides In Marine Microalgae And Its Mechanisms

Hormesis is a phenomenon characterized by dose-response relationships displaying low-dose stimulation and high-dose inhibition.In recent years,hormesis has attracted people's great attention;meanwhile,it has brought about a series of controversies.Large amounts of organosphosphorus pesticides applied in the agricultural practices and daily life have resulted in serious contamination in marine environment.Marine microalgae are the first primary producers in the marine ecosystem,playing a crucial role in maintaining the balance and stability of marine ecosystem.It has become a hot topic to study the hormesis caused by organophosphours pesticides on marine microalgae and its ecological risk.In this study,three widely-used organophosphours pesticides including glyphosate,dimethoate and trichlorfon,as well as eight typical red tide microalgae and feed microalgae were selected as experimental materials;some parameters indicating the growth,nutrient uptake,biochemical composition and photosynthesis of microalgae were determined so as to explore the hormesis induced by organophosphours pesticides on marine microalgae and its underlying mechanisms.Such fmdings will provide some basic data for in-depth understanding of the characteristics and mechanisms of hormesis; besides,they will provide a theoretical base for the application of organophosphorus pesticides, protection of marine bioresources and prevention of ecological risk resulted from organophosphorus contamination.1.Growth of eight representative marine microalgae including Skeletonema costatum, Heterosigma akashiwo,Phaeocystis globosa,Scrippsiella trochoidea,Chaetoceros sp., Phaeodactylum tricornutum,Dunaliella salina and Platyrnonas subcordiformis was investigated in low concentrations of organophosphorus pesticides of glyphosate,dimethoate and trichlorfon.The results indicated that the effects of low-concentration organophosphorus pesticides on growth of marine microalgae were dependent on the pesticide variety and microalgal species,and also related with culture time and pesticide concentration. Low-concentration organophosphorus pesticides could stimulate the growth,inhibit the growth or have no influence on the growth of marine microalgae.Obvious stimulation could be observed in the combinations of pesticides and microalgae including glyphosate-Skeletonema costatum, glyphosate-Heterosigma akashiwo,dimethoate-Heterosigma akashiwo,and trichlorfon-Platymonas subcordiformis,suggesting that it might be much more general for the red tide microalgae to be stimulated by low-concentration organophosphorus pesticides as compared with the feed microalgae.2.All the four combinations of pesticide and microalgae listed above were selected to further examine the characteristics and rules of hormesis induced by organophosphorus pesticides in marine microalgae.The results demonstrated that it might be a generalization that hormesis could be induced by organophosphorus pesticides in marine microalgae. Organophosphorus pesticides in low concentrations stimulated the growth of marine microalgae, while organophosphorus pesticides in high concentrations restrained the growth of marine microalgae.Moreover,there were significant timing and concentrations differences in the hormesis induced by organophosphorus pesticides in marine microalgae.3.Contents of inorganic P and N were measured in the culture medium of Skeletonema costatum and Heterosigma akashiwo treated with different glyphosate concentations.Our results showed that as compared with the high glyphosate concentrations,low ones promoted the growth of Skeletonema costatum and Heterosigma akashiwo;less consumption of inorganic P and N was found in low glyphosate concentrations.In general,there were higher inorganic P and N concents in the culture medium under 10 mg-L^-1 and 50 mg·L^-1 concentrations of glyphosate, whereas lower inorganic P and N concents under glyphosate concentrations of 0.1 mg·L^-1 and 1 mg·L^-1.4.Changes in the biochemical compositions including chlorophyll a,protein and carbonhydrate of Skeletonema costatum and Heterosigma akashiwo were studied under various glyphosate levels.The results implied that high concentrations of glyphosate remarkably decreased the contents of chlorophyll a,protein and carbonhydrate,but low concentrations of glyphosate potentially enhanced the contents of chlorophyll a,protein and carbonhydrate in two marine microalgae.The phenomenon of hormesis induced by organophosphorus pesticides in marine microalgae had been proved from the biochemical composition aspect in which alteration occurred in biochemical compositions under different glyphosate concentrations.5.Differences in the photosynthesis of Skeletonema costatum and Heterosigma akashiwo were compared in the presence of various glyphosate concentrations.The results suggested that high concentrations of glyphosate distinctly reduced the photosynthesis by decreasing the maximal photochemical effciency(Fv/Fm),actual photochemical efficiency(Yield),electron transport rate(ETR) and photochemical quenching(qP) of Skeletonema costatum and Heterosigma akashiwo.To some extent,low concentrations of glyphosate stimulated the photosynthesis of Skeletonema costatum and Heterosigma akashiwo by inceasing the chlorophyll fluorescence parameters mentioned above.