Marigold (Tagetes erecta L.) is a perennial edible medicinal plant. In order to test the allelopathic effect of marigold leaf extract on Chlorella vulgaris, the microalgae growth conditions under different concentrations of marigold leaf extract (0 to 50 g/l) were studied. The results showed that microalgal growth was inhibited by marigold leaf extract, and inhibition commonly increased with increasing concentration of the extract and culture time. The maximum inhibition rate (90.1%) appeared in leaf extract of 30 g/l after 14 days of incubation; marigold leaf extract induced chlorophyll degradation in algae cells, increased the permeability of cell membrane, and caused exudation of soluble protein and nucleic acid, leading to the damage of algae cell structure and metabolic dysfunction. The present results confirmed that marigold leaf extract has an allelopathic inhibition effect on C. vulgaris, and the results could be further applied to develop safe and efficient algaecides.

To evaluate the suitability of wastewater on the growth of alga Spirulina, reclaimed wastewaters, fishpond wastewater, industrial wastewater and mariculture water were used to culture Spirulina subsalsa and Spirulina platensis. S. subsalsa showed better adaptability to fishpond wastewater and higher specific growth rate than that of S. platensis. Thus, effects of factors such as the amount of baking soda, inoculation, and sodium nitrate on the growth, biomass and protein content of S. subsalsa were evaluated through the single factors design. Results showed that S. subsalsa had good growth under conditions of 4-12 g/L baking soda, 1-2 g/L NaNO 3 , 25-40°C, and 6000-12000 lux illumination. The maximum dry biomass and protein content were 3.48 g/L and 33.08%, respectively, suggesting that it was feasible to culture S. subsalsa in freshwater aquaculture wastewater.