Effects Of Microplastics And Antibiotics On Soil Physicochemical Properties,enzyme Activities And Microbial Community Characteristics In Greenhouse Soils

Microplastics and antibiotics are widely present in soil and the risk of contamination to soil ecosystems cannot be ignored.Although the environmental hazards of microplastics and antibiotics have received increasing attention from scholars at home and abroad,the effects of combined microplastic and antibiotic contamination in facility vegetable plot soils are currently unknown.In this paper,non-degradable polyethylene(PE)microplastics and degradable polylactic acid(PLA)microplastics were combined with the sulfonamide antibiotic sulfamethoxazole(SMZ)to investigate the effects of single and combined treatment of microplastics and antibiotics on the physicochemical properties,enzymatic activities and microbial community characteristics of the soil in vegetable farms.The main findings are as follows:(1)Soil physicochemical indicators are mainly influenced by the type and concentration of microplastics and their combination with antibiotics.The results of this study showed that high concentrations of PLA treatment significantly increased soil p H,while SMZ application alone did not have a significant effect on soil p H,but the combination of PLA and SMZ treatment(SPLA)had a significant effect on soil p H afterward.High concentrations of PLA significantly reduced soil conductivity and the lowest conductivity levels were found under the SPLA treatment at day 35,with a 49% decrease compared to CK.PLA and SPLA treatments significantly reduced soil nitrate-N content,while PE had no significant effect on soil nitrate-N content.Both high concentrations of PE and PLA significantly increased soil organic carbon content.(2)Soil enzyme activity was mainly influenced by the type and concentration of microplastics and in combination with antibiotics.SPLA treatment significantly increased carbon cycle-related β-glucosidase(BG)and β-xylosidase(BX)activities.PLA and SPLA treatments significantly increased nitrogen cycle-related urease and β-N-acetylamino glucosidase(NAG)activities.At 21 days of incubation,soil phosphatase(AP)activity was lowest at 2.99 nmol/g/h under the high PLA treatment,while AP activity was highest under the high SPLA treatment.(3)The soil microbial community was affected by a combination of microplastics and antibiotics.This study showed that the combined PE and SMZ treatment(SPE)reduced the richness and diversity of the soil bacterial and fungal communities under no straw addition and that SPE disturbed the soil microbial communities more significantly than PE application alone.Microplastic and antibiotic complexes under exogenous straw addition increased species richness,with SPLA having the highest diversity of soil microbial communities and containing the highest number of microbial endemic species.Microplastics altered the relative abundance of dominant microorganisms,but the extent varied with microplastic type,with significant differences between PLA and PE-treated soil microbial communities.The addition of microplastics and antibiotics directly affected specific taxa of the soil microbial community,with PLA increasing the abundance of Aspergillus and SMZ and SPE treatments decreasing the abundance of Aspergillus.There was very little similarity between the species composition of the soil microbial communities of the PE,PLA,and SMZ treatments.(4)The soil antibiotic resistance gene sul was affected by both microplastics and antibiotics.sul1 and sul2 abundance was significantly increased by SMZ,and SPLA in particular had a more significant effect on the abundance of resistance genes sul1 and sul2.The presence of PLA,especially SPLA,significantly altered the soil physicochemical properties and microbial community,thereby threatening soil health.Therefore,with the promotion and application of degradable plastics,the single and combined contamination effects of degradable microplastics and antibiotics have attracted sufficient attention.