Submerged macrophytes can effectively inhibit cyanobacteria bloom,which are dominated by Microcystis aerugi-nosa.However,whether the inhibitory effect of submerged macrophytes on M.aeruginosa depends on its density needs further investigation.In this study,dialysis bag method was used to form a co-culture system between Vallisneria natans(Lour.)Hara with three densities(1 000 g/m3,1 500 g/m3,2 000 g/m3)and M.aeruginosa with 8×104 cells/mL,4×105 cells/mL,8×105 cells/mL.The biomass,photosynthetic damage were analyzed.The results showed that when the M.aeruginosa density was 8×104 cells/mL,the inhibition effect of V.natans Lour.with 1 000 g/m3 was decreased by 91.73％,and the content of Chl-a and photosynthetic activity Fv/Fm of M.aeruginosa were decreased by 93.81％and 63.87％,respectively,compared to the control.Phycocyanin is severely damaged and has low engineering cost.When the M.aeruginosa density was 4× 10 5 cells/mL and 8×105 cells/mL,the inhibition rates of M.aeruginosa by V.natans Lour.with 1 500 g/m3 were 43.70％and 34.99％,respectively,and the content of Chl-α decreased by 67.39％and 44.27％,respectively,compared to the control.The photosyn-thetic activity Fv/Fm was decreased by 29.10％and 48.58％.Compared with V.natans Lour.,in the algae-grass coculture group with the planting density of 1 000 V.natans Lour.,the biomass of M.aeruginosa decreased by 30.36％and 35.71％in group of 4×105 cells/mL and 8×105 cells/mL M.aeruginosa,respectively,compared to the control,and the Chl-α content of V.natans Lour.was inhibited.Photosynthetic capacity decreased significantly.At the same time,photosynthetic activity Fv/Fm and Y(Ⅱ)values decreased with the increase of M.aeruginosa density.When the density of Microcystis aeruginosa in-creased to 4×105 cells/mL and 8×105 cells/mL,when the density of M.aeruginosa density was increased to 4×105 cells/mL and 8×105 cells/mL,planting of Vallisneria natans Lour.1 500 g/m3could achieve better algal inhibition effect,and the damage de-gree was small.This indicates that the mutual inhibition between species in the process of M.aeruginosa control and sub-merged plant restoration in lake ecosystems is density-dependent.In the process of controlling cyanobacteria bloom in the later stage,it is suggested that reasonable planning of planting density of submerged plants can achieve better restoration effect.
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