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The effects of pyrophosphate and polyphosphate on the growth of Microcystis aeruginosa and Chiorella pyrenoidosa were studied in unialgal cultures and in cultures separated by a dialysis membrane. M. aeruginosa and C. pyrenoidosa were able to similarly utilize pyrophosphate and polyphosphate, but their growth rates and cell densities were low in comparison with those in the orthophosphate controls. C. pyrenoidosa had a higher growth rate than M. aeruginosa in both unialgal and the separated cultures; moreover, C. pyrenoidosa had a greater ability to utilize phosphorus than M. qeruginosa. But because the C. pyrenoidosa population developed early but then declined, M. aeruginosa eventually became dominant in the separated cultures. Therefore, the interaction between M aeruginosa and C. aeruginosa might be complex because of an allelopathy effect, and nutrient competition is not the only factor determining species dominance in the phytoplankton assemblage. [ABSTRACT FROM AUTHOR]

Variations of bacterioplankton community composition were monitored during Microcystis spp. blooms in Lake Taihu using denaturing gradient gel electrophoresis (DGGE) of amplified DNA fragments from April through November in 2005. Two sampling sites were selected—one in Meiliang Bay and the other in the center of the western region of the lake. The average abundance of Microcystis spp. was higher in Meiliang Bay than in the lake center, while the bacterioplankton community diversity of Meiliang Bay was significantly lower than that of the lake center (P < 0.05). Comparison of DGGE profiles indicated that in Meiliang Bay bacterioplankton communities decreased in band richness and species diversity as Microcystis spp. abundance increased. In the lake center, DGGE band number and Shannon index reached their peaks when Microcystis spp. blooms declined. The Shannon diversity index for the bacterioplankton community was negatively correlated with the Microcystis spp. abundance (r = -0.53, P = 0.10). Changes in composition and biodiversity of the bacterioplankton community in the two regions of the lake were moderately correlated with Microcystis spp. bloom formations, which suggested a possible linkage between bacterioplankton community variations and phytoplankton blooms events. [ABSTRACT FROM AUTHOR]