Influence of dissolved aluminum on marine phytoplankton community structure and growth of Synechococcus sp.

We investigated the preliminary mechanisms of dissolved aluminum ( Al 3 + ) on marine phytoplankton through field and labo- ratory incubation experiments. Results from in situ experiments indicate that dissolved Al decreased the total abundance of micro-phyto- plankton by inhibiting the growth of cyanophyta Trichodesmium sp. ; the ratio of diatoms and dinoflagellates to total phytoplankton in- creased, leading to the change of micro-phytoplankton community structure. Whereas, the growth of Synechococcus was promoted after initial inhibition by Al, which resulted in the increasing of total abundance of pico-phytoplankton. Additionally, the stimulatory effects of Al on Synechococcus was observed under semi-continuous culture condition; especially in 20μmol·L - 1 Al-treated group, the signifi- cant promotion of total pico-phytoplankton abundance and growth of Synechococcus were detected ( P < 0. 05) . The growth of Synecho- coccus and the maximum quantum efficiency of photosynthesis II after long-term cultivation in dissolved Al were promoted by enhancing photosynthesis due to the increase of four photosynthetic pigments including phycoerythrin, phycocyanin, allophycocyanin and chloro- phyll a. The higher Al conditions resulted in higher growth rate in exponential phase and biomass in stationary phases as well as intra- cellular organic carbon accumulation.