Degradation Characteristics Of PLA/PBAT Degradable Microplastics And Their Biofilm Community Structure And Function Under Anthropogenic Environment

Microplastics exist extensively in microbial-driven Biogeochemistry cycles,and their surfaces are rich in a unique microbial community,forming a plastisphere.Compared with natural substrates,microplastics provide an additional carbon source for the development of biofilms,and the microbial community structure and function of biofilms will be different.As an important alternative to traditional plastics in reducing environmental pollution,the PLA/PBAT(Polylactic Acid/Polybutyrate Adipate Terephthalate)biodegradable plastic has been used more widely in human life.However,there are few studies on the microbial community characteristics and functions of plastic degradation process of different nutrient water.From the view of water environmental disturbance and microbial ecology,a biodegradable microplastic degradation(BMPs)experiment was established under different combinations of environmental elements,including the Control,N,Plant,Cut,Cut+N,Plant+N,and Nature groups in MoChou Lake,Nanjing,Jiangsu Province.The PLA/PBAT biodegradable microplastics were put into the mesocosm for 60 days to obtain 100 samples of microplastic biomembrane.High throughput sequencing,Fourier infrared spectroscopy,enzyme activity detection,and FAPROTAX functional prediction were used.Combined with the data of physical and chemical factors of water,the degradation characteristics,biofilm community composition,biodiversity,ecosystem function and its driving factors of PLA/PBAT biodegradable plastics were studied under different environmental conditions in MoChou lake.The following results were obtained:(1)The N addition and submerged plants changed the eutrophication state of the water,which showed that the N addition significantly increased the nitrogen content of water,while the presence of submerged plants significantly decreased the total dissolved phosphorus and nitrate nitrogen content.Eutrophication degree of water:Cut+N>N>Plant+N>Plant>Cut>Control>Nature.The degradation rate of plastics increases with eutrophication.The results were further confirmed by Fourier infrared spectra and scanning electron microscopy(SEM),that is,the groups containing N,such as N,Cut+N,and Plant+N groups,the hydrolysis of the ester group(1712cm-1)to hydroxyl group(3389.281cm-1)resulted in the increase of hydroxyl group content,and the change of hydroxyl group content of BMPs was positively correlated with nitrogen and phosphorus nutrition.Moreover,with the increase in degradation degree of BMPs,the bacterial diversity of BMPs increased,and the complex and diverse microorganisms were favorable for the degradation of microplastics.(2)BMPs bacteria shared a core microbiome:Proteobacteria,Firmicutes,Bacteroidetes,Actinobacteria,Planctomycetes,and Chloroflexi are the dominant phyla in each treatment.Principal component analysis(PCoA)and Venn diagram of bacterial genus showed the differences of BMPs bacterial composition,especially the genus distribution of Plant+N group was significantly different from other groups,which showed that the abundance of Rhodobacter was significantly increased.(3)It is noteworthy that the N addition significantly reduced the alpha diversity of BMPs bacteria,while the submerged plants significantly increased the bacterial diversity.With the increase of the degradation rate W(%)of microplastic,the bacterial diversity of BMPs increases,that is,the complex and diverse biofilms are beneficial to the degradation of degradable plastics.N addition and submerged plants significantly changed the network symbiosis pattern of BMPs bacteria,such as Cut group increased the competition relationship between bacteria.Oxidation-reduction potential,phosphate,total dissolved phosphorus,and total dissolved nitrogen were all important factors driving the BMPs bacterial community structure and diversity.(4)N addition and submerged plants significantly altered BMPs bacterial carbon,nitrogen,phosphorus,and sulfur-related enzyme activities.EMF:Plant+N>Cut+N>N>Cut>Nature>Plant>Control.Shannon diversity of BMPs bacterial was significantly correlated with C,N,P,S cycle ecosystem function,which was significantly positively correlated with carbon,nitrogen,and sulfur cycle enzyme activities,and significantly negatively correlated with acid phosphatase activity(P<0.05).pH,dissolved oxygen,reduction potential,chemical oxygen demand,nitrogen,and phosphorus are the dominant drivers of changes in EMF.The results of FAPROTAX functional prediction analysis showed that BMPs bacteria were mainly involved in chemoheterotrophic photoautotrophic metabolism processes and aromatic compound degradation,which are significantly correlated with total dissolved phosphorus,nitrate-nitrogen,phosphate,oxidation-reduction potential,pH,and other factors(P<0.05).In conclusion,the different combinations of nitrogen addition and submerged plants will cause a significant impact on the community structure and ecological function of BMPs biofilms.The surface of BMPs is a new niche for freshwater microorganisms,and increasing human activities and microplastic pollution have the potential to affect aquatic ecosystem function by altering biofilm metabolic activities.