| Biodegradable plastics refer to a type of plastic that can degrade into environmentally friendly substances through the action of microorganisms in nature.In recent years,biodegradable plastics have been widely used because they can be completely degraded after being discarded.However,the biodegradation process is a dynamic process,with the extension of degradation time,the molecular weight decreases gradually,and then smaller particles or fragments appear,that is,biodegradable microplastics.It is not completely clear whether biodegradable microplastics will have similar biological effects on plants as nondegradable microplastics.In this paper,biodegradable materials polylactic acid microplastics(PLA-MPs),butyleneadipate-coterephthalate microplastics(PBAT-MPs)were studied while nondegradable polyethylene microplastics(PE-MPs)and polypropylene microplastics(PP-MPs)were used as controls.Germination and pot experiments were conducted to explore the morphological changes of MPs before and after 20 d and 40 d of landfill,and their effects on soil dissolved organic carbon and physiological indexes,leaf transcription and metabolism of Brassica chinensis L..The main conclusions are as follows:(1)The surface of non-degradable microplastics PE and PP maintained good integrity at 20 d and 40 d,and the degradation traces were not obvious,while biodegradable microplastics PLA and PBAT were degraded,with different degrees of cracks and holes on the surface.The degradation degree of 40 d was greater than that of 20 d.The degradation degree of PL A-MPs was higher than that of PBAT-MPs.MPs had no significant effect on the content of DOC in root soil,but biodegradable microplastics could increase the content of DOC in soil at 40 d to some extent.(2)Neither biodegradable microplastics nor non-biodegradable microplastics had significant effects on the germination rate,root length,stem length,fresh weight and soluble sugar content of Brassica chinensis L.,but all four kinds of MPs inhibited the root activity at 20 d,and the inhibitory effects of PP and PBAT microplastics were more obvious at 40 d.MPs had no significant effect on chlorophyll content in leaves at 20 d,but only 2%PBAT-MPs and 0.2%PP-MPs treatments significantly decreased chlorophyll and carotenoid contents in leaves at 40 d.Different concentrations and kinds of MPs caused oxidative stress to different degrees,resulting in changes in antioxidant enzyme activities in leaves.MPs did not significantly affect the cell morphology of Brassica chinensis L.leaves,but the oxidative damage of leaf cells treated with biodegradable microplastics led to slight changes in cell membrane morphology.(3)Biodegradable microplastics cause Brassica chinensis L.leaves to produce more differential genes,and plant hormone signal transduction is the most important metabolic pathway for Brassica chinensis L.to cope with external MPs stress.Biodegradable microplastics PLA and PBAT had significant effects on MAPK signal pathway,brassinoid biosynthesis and glycosphingolipid biosynthesis-ganglion pathway at 20 d,and PLA and PBAT had significant effects on linolenic acid and linoleic acid metabolic pathways at 40 d,indicating that MPs had certain effects on hormone regulation,photosynthesis and oxidation-antioxidation system in Brassica chinensis L..(4)Biodegradable microplastics cause more differential metabolites in Brassica chmensis L.leaves.At 20 d all four kinds of MPs induced significant upregulation of glycosylphosphatidylinositol(GPI)-anchor biosynthesis,autophagy-others,vitamin B6 metabolism,poiphyrin and chlorophyll metabolism in Brassica chinensis L.leaves.Compared with non-degradable microplastics,biodegradable microplastics also led to up-regulation of glycerol phospholipid metabolism pathway and down-regulation of purine metabolism pathway.At 40 d,the addition of four kinds of MPs caused the down-regulation of purine metabolism pathway,and the biodegradable microplastics also caused the down-regulation of pyrimidine metabolism,monobactam biosynthesis,aminoacyl tRNA biosynthesis and linoleic acid metabolism.The results showed that MPs stress affected cell composition and structure,nitrogen and carbohydrate metabolism and nucleic acid formation,and biodegradable microplastics also had some effects on plant stress signal transduction,root tip morphology and plant pigment.(5)Biodegradable microplastics have a stronger effect on the transcription and metabolism of Brassica chinensis L.at the molecular level,but do not have a significant effect on the phenotypes of Brassica chinensis L.at the macro level,such as root length,stem length and fresh weight.So in the vegetable industry,we can consider using biodegradable agricultural film instead of traditional non-degradable agricultural film to reduce the problem of white pollution in the environment without affecting crop quality. |
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