Effects of iron availability on competition between Microcystis and Pseudanabaena or Chlorella species

Iron availability has been suggested to be one of the key factors limiting the formation of Microcystis sp. blooms in eutrophic lakes. However, the significance of competition of Microcystis sp. with other phytoplankton species under iron limitation is still unclear. Here, the competitive ability of Microcystis aeruginosa is reported from mixed cultures with Pseudanabaena sp. or Chlorella pyrenoidosa at two iron concentrations (pFe 21.4 and 20.3). In monoculture, low iron conditions caused a smaller decrease in maximal relative electron transport rate, PSI/PSII fluorescence ratio and phycocyanin content in M. aeruginosa than in Pseudanabaena sp. The same iron concentration resulted in a significant decrease in chlorophyll a content, PSI/PSII fluorescence ratio, and maximal PSII photochemical yield in M. aeruginosa but there was no change in these factors in C. pyrenoidosa. All three species were more vulnerable to photoinhibition under low iron conditions. Iron limitation also decreased their cellular vol...