| Human activities resulted in ozone layer depleted or even ozone hole, which allows enhanced UV-B radiation to the ground and further influenced the survival of hunman and other organisms. UV-B radiation is able to penetrates water system as well, threatening marine oganisms especially plankton. The United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO) announced that the ozone layer were thickened 4% during 2000-2013, and the ozone hole over Antactica stopped expanding. Still, the ozene layer thickness is 6% lower compared to 1980s, there is a long way to go for it to recover. So the impact of UV-B radiation should not be negleted.Polybromodiphenyl Ethers (PBDEs) are series of new-kind Persistant Organic Pollutants (POPs), which have properties of difficult-degration and long-distance migration, and can concentrate through the food chain. Now detected to exist in the atmosphere, water, sediment, plant, animal and human body, PBEDs have become global enviorenmental pollutants. Studies demonstate that PBDEs have neurotoxicity, reproductive and development toxicities and immunotoxicity to organisms.Marine microalgae are the most primary producer, and also have an important impact on the composition and variation on marine ecosystem. Many studies have been carried out about the response of marine microalgae to UV-B radiation, however, there is not much research concerning PBDEs in our corntry, much less the combined effects of BDE-47 and UV-B radiation to microalgae. Thus, discussion regarding to combined effects of BDE-47 and UV-B radiation on the growth and photosynthetic physiology has practical significance, and can provide theoretical basis for self-protection as well as adaption of microalgae when exposed to BDE-47 and UV-B radiation.In this study, Karenia mikimotoi was used as a target, exposed to BDE-47, UV-B radiation and combined effects, respectively. The changes of group growth and parameters of photosynthetic physiology were determined. Results show that:1.The effects of UV-B radiation on population growth and photosynthetic physiology of Karenia mikimotoiThe relative growth rate was decreased when exposed to UV-B radiatiom, population growth was inhibited as UV-B radiation elevated, and 96h EC50 is 184.111J m-2 d-1. Content of chlorophyll a was reduced resulted from enhanced UV-B radiation. According to analyse of rapid light curves and induction curve parameters, UV-B radiation elevated the tolerance of light intensity, altered the pathway of excess energy.48h exposure promoted the relative electron transport rate, CO2 fixation and energy transformation.96h low-dose exposure induced excess energy to dissiparate though non-photochemical quenching as heat.2.The effects of BDE-47 on population growth and photosynthetic physiology of Karenia mikimotoiBDE-47 had a significant negative impact on the population growth of Karenia mikimotoi,96h EC50 is 0.1 10mg L-1. As concentration elevated, the inhibiting effect increased. So as the synthesis of chlorophyll a. Tolerance of light intensity was strengthened when exposed to BDE-47, whereas solar energy utilization efficiency and maximum photosynthesis rate were reduced, excess energy dissiparated through non-photochemical quenching as heat.3.Combined effects of BDE-47 and UV-B radiation on population growth and photosynthetic physiology of Karenia mikimotoiThe inhibition of Joint effects were much stronger than single, both to population growth and synthesis of chlorophyll a, the group stopped grow from start. Light energy utilization efficiency declined, the pathway of exceed light energy dissiparate was changed as well, the maximum potential photosynthetic rate was decreased in 48h, the actual photosynthetic rate was decreased in 96h, but Tolerance of light intensity was not significately impacted. |
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