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Effects Of Microplastics On Soil Microbial Diversity And Organic Carbon-Degraded Enzyme Activites

Posted on:2022-08-13Degree:MasterType:Thesis
Country:ChinaCandidate:Q Q GuoFull Text:PDF
GTID:2480306335455754Subject:Agronomy
Abstract/Summary:PDF Full Text Request
Microplastic pollution has become a global ecological and environmental problem.It is estimated that the accumulation of microplastics in terrestrial ecosystems is much greater than that in marine ecosystems.However,the current research on microplastics in soil focuses on quantitative statistics and source analysis,while research on the effects of microplastics on soil properties and functions is very lacking.At the same time,the mechanism of microplastics affecting soil health is still unclear.Based on this,this research focuses on microplastics and soil biological properties,discusses the effects of microplastics on soil microbial diversity and the activity of organic carbondegraded enzymes,then reveal the mechanism by which microplastics affect the accumulation of natural organic carbon in soil.At the same time,this study also discussed the effect of heat treatment on the biological properties of microplastics contaminated soil and the restoration of natural organic matter.In this study,two types of microplastics were added to the soil,namely polyester microfibers(PMF,0%,0.1%,0.3% and 1.0% dry soil weight)and low-density polyethylene film(LDPE,0%,0.1% and 0.3% soil dry weight).In addition,polyester microfibers were added to the soil for heat treatment(HPMF,0%,0.1%,0.3% and 1.0%soil dry weight),and then natural organic matter(OM,black poplar(Populus nigra)leaf litter,0%,1% and 3% soil dry weight)for indoor cultivation experiments.Highthroughput sequencing technology was used to analyze the diversity of soil microorganisms,and enzyme-labeled method was used to determine the activity of soil organic carbon-degraded enzymes: sucrase(SR),amylase(AL),?-xylosidase(?-XD),?-glucosidase(?-GD),cellulase(CL)and laccase(LC).The main findings are as follows:(1)The effects of the addition of PMF and OM on soil microbial diversity and the activity of organic carbon-degraded enzymes were explored,and the effect of PMF on the accumulation of soil natural organic carbon and its mechanism were revealed.The results showed that the addition of PMF significantly increased the diversity of soil fungi,but it had no significant impact on the diversity of soil bacteria;the addition of PMF significantly increased the activity of soil laccase.At the same time,the diversity of bacteria and fungi on the surface of polyester microfibers and the relative abundance of aerobic bacteria are higher than those in the surrounding soil.The addition of PMF had no significant effect on the microbial community structure(phyla and genus level)and the stability of the bacterial community in the soil and on the surface of polyester microfibers.However,the addition of OM affected the microbial community structure(genus level)and enzyme activity of the microplastic contaminated soil,and improved the stability of the bacterial community.The addition of high concentrations of PMF significantly reduced the accumulation of natural organic carbon.These findings indicate that the addition of PMF improves the diversity of soil fungi and laccase activity.At the same time,the surface of polyester microfibers had higher microbial diversity and abundance of aerobic bacteria,which may be the reason for the decrease in the accumulation of natural organic carbon in the soil.(2)The effects of HPMF on soil microbial diversity and the activity of organic carbon-degraded enzymes were explored,and the restoration effect of the addition of OM after heat treatment on the soil contaminated by microplastics was further analyzed.The results showed that high concentrations of HPMF significantly increased the diversity of soil bacteria,but heat treatment had no significant effect on the diversity of fungi.High concentrations of HPMF significantly reduced soil laccase and cellulase activities,but there was no significant difference in the activities of other organic carbon-degraded enzymes between different HPMF treatments.Comparing the HPMF treatment with the corresponding PMF treatment,it was found that the diversity of soil bacteria and fungi remained unchanged,but the microbial community structure and the activity of organic carbon-degraded enzymes changed.The addition of OM improves the stability of the bacterial community,but HPMF still affects soil microbial diversity and enzyme activity.HPMF significantly reduced the accumulation of natural organic carbon.These results indicate that polyester microfibers still affect soil microbial diversity and enzyme activity after heat treatment.The addition of OM did not eliminate the impact of HPMF on soil biological characteristics,and HPMF still affects the accumulation of soil natural organic carbon.(3)The effects of the addition of LDPE and OM on the activity of organic carbondegraded enzymes in soil aggregates of different particle sizes were explored.The results showed that there was no significant difference in the activity of organic carbondegraded enzymes in total soil and soil macro-aggregates between different LDPE treatments.At the addition level of 3% OM,the addition of LDPE significantly improved the activity of organic carbon-degraded enzymes in the micro-aggregates.The addition of LDPE had no significant effect on the accumulation of natural organic carbon in the soil.These results indicate that the addition of LDPE had no significant effect on soil organic carbon-degraded enzyme activity,making the accumulation of natural organic carbon unchanged,but the addition of LDPE and OM improves the enzyme activity of degrading simpler carbon-containing compounds in soil microaggregates.This study shows that the addition of polyester microfibers increased the microbial diversity in the soil and the surface of the polyester microfibers,and at the same time increases the activity of soil laccase.The polyester microfibers still affect the soil microbial diversity and laccase activity after heat treatment.And the addition of natural organic matter did not eliminate the influence of polyester microfibers after heat treatment.Regardless of whether the polyester microfiber is heat-treated or not,the accumulation of natural organic carbon in the soil is reduced.The synergistic effect of low-density polyethylene film and natural organic matter promotes the excitation effect of soil micro-aggregates.
Keywords/Search Tags:microplastics, soil microorganisms, soil enzyme activity, organic carbon
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