Sediments are important sites for cyanobacteria overwintering,and also be the sinks of microplastics(MPs)and nutrients.In this study,a laboratory experiment was conducted to explore the effects of biodegradable poly lactic acid microplastics(PLA-MPs)on the recruitment of dormant cyanobacteria from sediment.Different content(0,0.05％,0.5％,5％,w/w)of PLA-MPs were added to the sediment and then incubated under 15℃,with light intensity of 40μE/(m2.s)for 50days.Results showed that addition of 0.5％and 5％of PLA-MPs significantly increased the concentrations of NH4+-N and NO3--N(P＜0.05)in the overlying water,which was 61.19 and 84.94 times,5.80 and 17.01 times higher than that in the control,respectively.This was linked with the increase in the abundances of nitrogen fixation(nifH),nitrification(AOB-amoA、nxrB)and the reduction of denitrification(narG)genes.Besides,the abundance of the phoD gene that involved in organophosphorus mineralization,the oxygen penetration depth in sediment were also decreased with the presence of PLA-MPs,which probably promote the release of sedimentary phosphorus.Moreover,the relative abundance of the cyanobacterial phylum in the water increased significantly with the increase in PLA-MPs content,which was 12.38％,23.53％and 28.54％higher than that of the control group,respectively,indicating that PLA-MPs promoted the recruitment of sedimentary cyanobacteria.These findings may extend the current understanding of the potential aquatic risk of biodegradable PLA-MPs.
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