[Effects of species richness on colony biomass and tests of sampling- and complementary effect]

With eight species of unicellular algae cultured in random combinations to construct the assemblages with different degrees of richness, the increase pattern of colony biomass with the change of species richness was investigated, and the sampling effect was detected by using multiple variance analysis (MANOVA) method. Three analysis methods, i. e., over-yielding analysis, relative yield total (RYT) index, and subset approach, were applied to explore the complementary effect, and additive partitioning method was applied to separate the sampling effect and complementary effect quantitatively. The results showed that the colony biomass presented a saturated rise with the increase of species richness, and a strong complementary effect was observed in phytoplankton colonies. At exponential growth phase, some specific algal species affected the colony biomass significantly, but after reaching the stable phase, the biomass was not affected by the presence of given phytoplankton. The sampling effect was generally negative at stable phase, while the complementary effect and net biodiversity effect were always positive.