Effect Of Microplastics On The Chemical And Biological Properties Of Maize Cultivated Soil And Maize Growth

Microplastics pollution has been ranked as the second most significant scientific issue in the field of environmental and ecological research,at the 2nd United Nations Environment Assembly in 2016.Due to human activities and the transportation of environmental media,soil has become the largest repository for microplastics.In recent years,the threat of microplastics to soil ecosystems has attracted widespread attention from scholars both domestically and internationally.The contamination of microplastics in agricultural soil,its effects on soil properties,microorganisms,and plants and animals,has become a research hotspot.This study conducted a short-term pot experiment building upon a field investigation of the presence of microplastics in farmland soil in Baotou city.By externally adding microplastics particles with different concentration gradients,simulating varying degrees of microplastics pollution in farmland soil,the study aimed to investigate the impact of microplastics on soil chemical and biological indicators,soil microbial communities and maize growth.The main findings of the study are presented below:1.The concentration of microplastics in agricultural soils at sampling points was found to be 24666.67±12950.76 n/kg in the plow layer.Microplastics with particle sizes below 100 μm were predominant,accounting for over 90% of the total microplastics content.Polyamide(PA)and polyethylene(PE)were identified as the main microplastics components,representing 67.56% and 10.68% of the total microplastics content,respectively.2.Microplastics have complex impacts on both chemical and biological characteristics of soil.Microplastics significantly affect soil chemical properties,with a significant positive correlation found between soil organic matter and microplastics concentration(increases of 2.80%,30.37%,88.10%,118.22%,and 126.52% observed in each concentration treatment group compared to the control group).Microplastics were found to suppress soil total nitrogen,nitrate nitrogen,ammonium nitrogen,available phosphorus,dissolved organic nitrogen,and dissolved organic carbon to some extent.The highest concentration treatment decreased these parameters by 31.14%,22.75%,12.50%,43.85%,36.24%,and 6.25%,respectively.Soil p H was inhibited within a certain concentration range before being promoted.The effects of microplastics on soil microbial biomass and soil enzyme activities were complex.Soil microbial biomass in the microplastics-added treatment groups were suppressed at low concentrations(0.5%)and promoted at high concentrations(5%-10%).Soil enzyme activity in the microplastics treatment group was generally higher than that in the control group.Most soil enzyme activities were positively correlated with microplastics concentration in the low-to-medium concentration range(0.5%-2.5%),but decreased in the high concentration range.Moreover,soil enzyme activity in the rhizosphere was found to be more sensitive to microplastics concentration than that in the bulk soil.3.In short-term pot experiments,microplastics have a significant impact on the bacterial and fungal communities in both rhizosphere and non-rhizosphere soils.The analysis of community structure and diversity showed that the number of dominant bacterial species of the genus and phylum levels was higher in rhizosphere soils than in bulk soils,and the fungal community structure at the order level in rhizosphere soils was more similar to that in mixed soils.Moreover,the differences in bacterial community between rhizosphere and bulk soils were more significant than those in fungal community,particularly in different concentration microplastics treatments.Analysis of microbial community diversity showed that the trends of changes in α-diversity of bacterial and fungal communities were similar,and the microbial community differences between different concentration microplastics treatments were significant and well-grouped,with significant differences between rhizosphere and bulk soils.The co-occurrence network showed that microplastics had a greater impact on the bacterial community in the rhizosphere soil than in the bulk soil,and the fungal cooccurrence network in rhizosphere and bulk soils differed significantly.This study highlights the important role of rhizosphere soil in investigating the impact of microplastics on soil microbial communities and ecological functions,and further attention should be paid to the monitoring of rhizosphere soil in future research on soil microplastics.4.Microplastics pollution has negative effects on the growth,development,and biomass accumulation of maize(Zea mays L.).The results of the study showed that microplastics treatment significantly affected the biomass accumulation of individual maize plants,with a reduction of 53.60%,52.95%,46.39%,38.20%,and 47.54%compared to the control group.In the short term(0-7 days),there were no significant differences in maize height and leaf area due to microplastics exposure.However,at day 14,there was a trend of promotion followed by inhibition of maize height and leaf area with increasing microplastics concentration in the treatment group.Correlation analysis showed that microplastics pollution affected maize growth by affecting the chemical and biological characteristics of the soil indirectly.In conclusion,based on a comprehensive assessment of soil chemical and biological characteristics,microbial communities,and plant growth,microplastics pollution may have irreversible negative effects on agroecosystems and exhibit a strong concentration-dependent effect.This study provides new evidence for the presence and risk assessment of microplastics in agricultural soils and sheds new light on the response mechanisms of agroecosystems to microplastics pollution.