Study On The Impact Of Exogenous Biochar On Microplastic-Soil Ecosystem And Its Response Mechanism

Due to the extensive use of plastics,microplastics accumulate extensively in agricultural soils and pose a great threat to soil environmental health.Although an increasing number of studies have reported the effects of microplastics on soil ecosystems,there is still a knowledge gap regarding the ecological impacts of microplastics on the soil environment and their management.Biochar is a commonly used environmental functional material that acts as a soil conditioner to enhance soil ecological functions and elemental transformation processes.Therefore,biochar is often exposed to soil at the same time as microplastics.However,little is known about whether biochar input affects changes in soil properties under microplastic exposure and how it affects the ecological mechanisms of microbial community composition,structure,assembly,and metabolic functions.In this study,the effects of microplastic pollution on soil properties and its microbial communities were investigated by soil incubation experiments using high-throughput sequencing technology,and the effects of biochar on soil properties,key enzyme activities,soil microbial communities and their functions were also explored to reveal the response mechanisms of soil ecosystems to microplastics and to provide important insights into the use of biochar to regulate microplastic-contaminated soil environments.(1)Clarified the main physical and chemical property indicators and key enzyme activities(urease,acid phosphatase and fluorescein diacetate hydrolases)of the soil are differently affected by the type and dose of microplastics in soils incubated with different concentrations of conventional plastics(polyethylene)and biodegradable plastics(polylactic acid).Microplastics affected the soil nitrogen conversion process:polyethylene increased soil urease activity by 70-123%,polylactic acid increased urease activity by 21%-44%;at the same time,polyethylene treatment increased soil soluble organic carbon content by 65%,polylactic acid increased by 80-110%,thus changing the soil microbial biomass.Especially when the microplastic pollution was 5%(w/w),polylactic acid microplastics decreased soil p H by 15%and increased soil dissolved organic carbon content by 50%,which indicated the impact of high concentrations of microplastics on soil environmental properties larger,where the impact of degradable microplastics is more pronounced.On the other hand,using alpha and beta diversity calculations,species composition and co-occurrence network analysis for soil microbial communities,it was shown that microplastics changed the composition and structure of soil microbial communities(p<0.05),enzyme activity,and environmental factors.There is an interaction relationship with microorganisms(the Pearson analysis coefficient is close to 1or-1),which is an important driving factor for soil ecosystems to respond to microplastic stress.The results showed that polyethylene microplastics had a more significant impact on soil bacterial communities,while polylactic acid microplastics had a greater impact on fungal communities.The overall performance was that the soil indicators were more sensitive to high concentrations of degradable microplastic polylactic acid.(2)Preliminarily revealing the response mechanism of biochar regulating microplastic soil ecosystem.Compared with the control,whether it was polyethylene or polylactic acid microplastic soil,the application of biochar increased the soil acidity by 15%～21%,the soil DOC content almost doubled,and the content of nitrate nitrogen decreased and the ammonium state increased.Thereby,it improved nitrogen utilization.On the other hand,biochar application significantly changed the diversity of soil microbial communities and their functions(p<0.05).Biochar altered the relative abundance of soil species,including an 18%increase in the abundance of Bacteroidetes and 16%decrease in the abundance of Nitrifying bacteria,thereby affecting the function of the soil bacterial community and altering the biomarkers of the bacterial community.In addition,biochar increased the niche width of the bacterial community and strengthened the role of stochastic processes(R~2>0.5)in microplastic-contaminated soils.The network relationship of biochar soils was tighter and more competitive,and these effects showed to be more sensitive to the accumulation of biodegradable microplastic polylactic acid in soil,thus having a greater impact on its ecosystem.The study highlights the difference in bacterial composition and function before and after the application of biochar in soil ecosystems polluted by microplastics.The recovery and detection of microplastics found that biochar exacerbated the degradation and cracking of soil microplastics,indicating that the application of biochar has a positive effect on soil.The role of improving soil quality and mitigating microplastic pollution is expected to provide information for exploring biochar to help prevent and control soil microplastics.