Combined Effects Of Enhanced UV-B Radiation And Enriched CO₂ On Marine Microalgae

Atmospheric levels of CO2 are expected to double during the 21st century. In addition to CO2, chlorofluorocarbons (CFCs), CH4 and N2O are also increasing with industrialization. The increase of these trace gases is expected to deplete the stratospheric ozone column with a subsequent increase in the amount of solar UV-B radiation reaching the earth. Both CO2 and UV-B radiation are expected to increase simultaneously with future changes in global climate. UV-B radiation can significantly damage microalgae. The main targets are protein, DNA and photosynthetic pigments, and so on. Elevated CO2 concentration can promote the biomass, photosynthesis of microalgae, while combined effects of UV-B radiation and enriched CO2 on marine microalgae have not been reported. In this article, we take several species of marine microalgae as experimental objectives, and discuss the mechanisms of enhanced UV-B radiation and enriched CO2 on the physiological ecology and cytology of marine microalgae by studying enhanced UV-B radiation, elevated CO2 singlely and CO2 /UV-B radiation in combination, to supply experimental base for aquatic ecosystem with changes in global climate. Through experiments, we get results as follows:1. UV-B radiation inhibited the growth of marine microalgae, and the inhibiting action increased as increasing UV-B radiation dosage. Under the condition of solitary cultivation, the sensitivity of short-term (2d) UV-B radiation on solitary cultivated eight species of microalgae was Skeletonema costatum Greville < Platymanas sp. < Dunaliella salina < Chlorella.sp< Chaetoceros miielleri Lemmermann < Platymonas subcordiformis < Nitzschia clostertium< Isochrysis galbama Park 8701.Elevated CO2 can promote the growth of marine microalgae, and as the time was prolonged, the increase amplitude was greater. The sensitivity of six species of algae to elevated €62 was Chlorella. s p < Dunaliella salina< Isochrysis galbama Park 8701 < Nitzschia clostertium< Platymonas subcordiformis< Platymanas sp.2. The effects of three UV-B radiation doses (0, 2.88 J/m2, 5.76 J/m2) on competitivebalance of three species of algae under the condition of mixed cultivation were examined. The total biomass of three species of microalgae under the UV-B dosage of 2.88 J/m2, 5.76 J/m2 was greatly reduced, and the competitive balance changed also. The experiment showed that, the sensitivity of UV-B radiation on three species of microalgae was Isochrysis galbama Park 8701>Nitzschia clostertium >Platymonas subcordiformis. So enhanced UV-B radiation provide competitive dominance for Platymonas subcordiformis, which has high tolerance to UV-B, and in general, the effect of UV-B was in favor of Platymonas subcordiformis. On the 21st day, in the treated groups of UV-B radiation (2.88 J/m2, 5.76 J/m2), Platymonas subcordiformis became the dominant algae.Compared with low concentration COi, elevated COi promoted the growth of three algae, and elevated COa changed the sensitivity of three species of algae under the condition of mixed cultivation, comparing to under the condition of solitary cultivation. On the 21st day of the experiment, the dominant algae, subdominant algae and rogue algae were not changed.Compared with control (air), enhanced UV-B + elevated CO2 greatly decreased cell densities of three species of algae. Therefore, although elevated CO2 can promote the growth of algae, it can not counteract the effect of UV-B radiation on biomass of marine microalgae. Compared with control (air), enhanced UV-B + elevated COa changed the interspecific comptition and dominant algae.3. Effects of enhanced UV-B radiation (not bubbling) on the ultrastructure of Dunaliella salina were examined. After exposure to enhanced UV-B radiation, dramatic ultrastructual changes occurred in the chloroplast of D. salina; some cristae of mitochondria were disintegrated; the thylakoid penetrating into the pyrenoid was lost or broken. After exposure to enhanced UV-B radiation, enhanced UV-B radiation caused the accumulation of starch grains and lipid globu...