Effects Of PPC Film Mulching On Soil Community And Screening Of Pro-degrading Strains

As a special farmland management measure,plastic film mulching has the characteristics of water retention and heat preservation,which affects the agricultural production methods in the low water consumption and water shortage areas in the world,and improves the crop yield in these areas.The main component of conventional plastic film is polyethylene,which is extremely difficult to degrade under natural conditions.The thin film can be easily broken in the farmland after use,and difficult to recover.With the continuous extension of plastic film mulching years,plastic film residues accumulate in the soil year by year,causing serious pollution to the farmland environment.Polypropylene carbonate（PPC）is a new type of biodegradable plastic produced by the"alternative"copolymerization of carbon dioxide and propylene oxide（PO）,and the final products after its degradation are H₂O and CO₂,and it can effectively improve and alleviate the pollution of traditional polyethylene farmland residual film.However,due to the strong hydrophobicity of PPC,microorganisms cannot easily attach to its surface,resulting in a slow degradation rate,and thus PPC is unable to exert its environmental protection properties.Therefore,how to improve the degradation efficiency of PPC plastic film is a hot research direction.At present,there are few studies on the effect of PPC film mulching on soil and soil microbial communities,the biodegradation process of PPC film,and PPC film-degrading strains.Therefore,this paper uses high-throughput sequencing to investigate the effect of PPC plastic film mulching on soil and soil microbial community and the dynamic changes of soil microbial community in the degradation of process of PPC plastic film,and also screen strains suitable for PPC plastic film degradation,to provide scientific basis and theoretical basis for the soil safety of PPC plastic film and the large-scale use of biodegradable plastic film in the future.In this paper,the changes of farmland soil physicochemical properties（pH,EC,SOC,AP,AK）under the condition of PPC film mulched and unmulched were explained,and differences among microbial community abundance,diversity,composition,and structure were explored in depth.The microbial communities that are mainly involved in the degradation of PPC mulch film biodegradation and the dynamic changes of microbial communities in different degradation time were explored,and the metabolic functions of microorganisms were predicted.The microbial strains with the biodegradation function of PPC film were also screened and identified and the degradation performance of the strain on PPC plastic film was evaluated by the growth,weight loss percentage,water contact angle（WCA）,scanning electron microscope（SEM）and Fourier transform infrared spectroscopy（FTIR）of the strain.The main conclusions are as follows:（1）Film mulching increased soil pH and decreased EC and SOC contents,among which pH and SOC were the most important factors affecting bacterial and fungal community changes.Film mulching also increased the relative abundance of Acidobacteria at the phylum level and the genus MB-A2-108 at the genus level,reducing the potential risk of soil pathogens to a certain extent.Although PPC mulching did not significantly affect the overall abundance and diversity of the community,it increased the correlation and complexity of microbial communities.（2）During the degradation of PPC plastic film,the dominant species at the phylum level were Proteobacteria（61.6%）,Bacteroidota（24.1%）and Actinobacteriota（7.2%）;the dominant species at the genus level were Pseudomonas（18.1%）,Flavobacterium（10.0%）and Rhizobacter（7.4%）.The relative abundances of Proteobacteria and Actinobacteriota increased from 41.4%and 5.4%to 66.6%and 22.1%,respectively,and Bacteroidota decreased from 45.8%to 4.5%from the mid-degradation stage to the late stage of PPC mulching;at the genus level,the relative abundance of Rhizobacter The relative abundance of Flavobacterium increased from 5.1%to 17.8%,the relative abundance of Flavobacterium decreased from 32.0%to 0.7%,and the relative abundance of Pseudomonas increased from 6%to 14.3%and then decreased to 3.8%.The relative abundances of Paenarthrobacter＿nitroguajacolicus and Rhodanobacter＿sp increased from 4.9%and 1.5%to 21.5%and 10.4%,respectively,at the end of degradation.These two strains may be involved in the main degradation of PPC plastic.The prediction of metabolic function in the degradation process of PPC plastic film shows that Hydrocarbon＿degradation and Aromatic＿hydrocarbon＿degradation may play a major role in the early stage of degradation,and Plastic＿degradation may play a major role in the entire degradation process.（3）Through the screening of strains in the soil paved with PPC film,a bacterium J16 that belongs to Bacillus with high degradation efficiency was selected,it has 100%similarity with Bacillus subtilis and has good biodegradation potential for PPC film.The growth of J16 strain under the condition of co-cultivation with PPC film as the sole carbon source indicated that the strain can utilize PPC as the sole carbon source.SEM surface performance analysis showed that the roughness of the PPC film increased and obvious holes appeared.WCA analysis showed that the surface hydrophobicity of the PPC film decreased.FTIR spectral analysis showed that the structure of the functional group of PPC changed.And the weight percentage of PPC decreased,which further determined the degree of degradation of PPC.Taken together,Bacillus subtilis J16can degrade PPC film.