Pollution Characteristics Of Microplastics In Tobacco-growing Soil And Its Effects On Growth And Development Of Flue-cured Tobacco

In this study,tobacco-growing soil in Wulong of Chongqing and Guangyuan of Sichuan was selected as the research object.By density flotation method,microplastics were extracted from the soil.The type,abundance,particle size and area of microplastics were observed and recorded under a microscope,so as to clarify the distribution characteristics of microplastics in topsoil in Wulong of Chongqing and Guangyuan of Sichuan.Through pot simulation experiment,three treatments were set up: no microplastics（CK）,0.1% microplastics（T1）and 1%microplastics（T2）.The effects of different residual amounts of microplastics in soil on the growth and development of flue-cured tobacco and soil properties were analyzed,and the ecological effects of microplastics on tobacco were explored.The results are as follows:（1）The soil microplastics abundance ranges from 0.4×10² pieces·kg^-1 to37.3×10² pieces·kg^-1 and from 1.20×10² to 8.9×10² pieces·kg^-1 in Wulong of Chongqing and Guangyuan of Sichuan,respectively.The average abundance was（7.91±1.06）×10² pieces·kg^-1 and（4.81±3.53）×10² pieces·kg^-1,respectively.The average area was（11.26±1.96）×10² mm2·kg^-1 and（4.45±4.98）×10² mm2·kg^-1,respectively.There are four types of microplastics in soil: film,debris,foam and fiber,and the largest proportion is film.There are two kinds of color,black and transparent,the most proportion is transparent.The average particle sizes of the four kinds of microplastics in Wulong tobacco field of Chongqing were 1.85,1.48,1.63 and 2.48 mm,respectively.The particle sizes were mostly between [1-2)mm,and the areas were mostly between [0-1)mm2·pieces-1.The average particle sizes of the four kinds of microplastics in Guangyuan tobacco field soil of Sichuan Province were 1.18,1.12,1.69 and 2.14 mm,respectively.The particle sizes were mostly between [0.5-2] mm,and the areas were mostly between [0-1)mm2·pieces-1.The proportion of microplastics in the area of [0-1)mm2·piece-1 was 19.05%,which was significantly lower than the proportion of microplastics in the corresponding range（70.32%）.The amount of microplastics in soil samples increased with the decrease of the area,and the decrease of the area was accompanied by the increase of the amount of microplastics.（2）The addition of microplastics had no significant effect on the growth and development of tobacco plants in the early stage,but aggravated the disease of tobacco plants in the late stage,increased the value of chlorophyll a/b,enzyme activity of antioxidant system and soluble protein content,and caused stress on the growth of tobacco plants.The stress effect of flue-cured tobacco was enhanced with the increase of microplastics addition concentration.But the addition of microplastics promoted the accumulation of mineral elements in the tobacco plant.（3）Microplastics input carbon sources into soil and increase soil organic matter content,but have no significant effect on other soil nutrients.The addition of microplastics increased the number of soil bacteria,fungi and actinomyces.Moreover,the Chaol index of bacteria and fungi in rhizosphere soil was increased,and the diversity and abundance of soil microorganisms were improved.The increase degree of low concentration microplastics（0.1%）was higher than that of high concentration microplastics（1%）.Low concentration of microplastics increased the utilization rate of soil microbial carbon sources,while high concentration of microplastics decreased the utilization rate of soil microbial carbon sources.At the level of bacteria,Proteobacteria,unidentified_Bacteria,Cyanobacteria and Firmicutes were the main dominant bacteria in soil.At the fungal phylum level,Ascomycota,Basidiomycota and Mortierel were the dominant phylum in soil.Fusarium added microplastics treatment increased significantly.The results showed that microplastics in soil could stress the growth of tobacco plants and inhibit the growth of tobacco plants.Low concentration of microplastics（0.1%）was beneficial to improve the diversity of soil microbial community and microbial carbon source utilization rate,but high concentration of microplastics reduced the microbial carbon source utilization rate and increased the abundance of Fusarium in soil.