[Effect of Low-density Polyethylene Microplastics on Soybean-soil-microbial System].

Abstract

The widespread use of plastics has led to the prevalence of microplastics in the soil environment, which, as an emerging pollutant, affects plant growth, soil physicochemical properties, and microbial community structure. The effects of different contents of low-density polyethylene microplastics （LDPE-MPs） on soybean growth, soil physicochemical properties, soil enzyme activities, and microbial activities were investigated through pot culture experiments to explore the toxic effects of microplastics on soybean-soil-microbial systems. The results showed that compared with that in the control, microplastics inhibited soybean emergence （14.1%-25.0%）, whereas plant height, biomass, and pod weight were inhibited by low concentration and promoted by high concentration, and SPAD of soybean was significantly reduced by high concentrations of microplastics stress. Microplastics affected the quality of soybeans, with s-sugars, s-proteins, and cellulose increased by 117.7%-258.8%, 3.7%-61.6%, and 47.8%-83.4%, respectively, compared with those in the control. Microplastic addition also affected soybean nutrient uptake, as evidenced by the promotion of N （95.1%-144.4%） and P （4.1%-20.4%） uptake in the above-ground portion of soybeans and N （11.4%-19.4%） and P （8.5%-42.6%） uptake in the below-ground portion of soybeans, and inhibited K （2.2%-15.3%） uptake in the aboveground portion of the plant and K （3.9%-9.4%） uptake in the below-ground portion of the plan, respectively. The addition of microplastics had little effect on soil pH； however, it significantly increased CEC （65.1%-74.7%） and SOM （22.6%）. With the increase in the addition content, the content of NO₃^--N, AP, AK, and UE activities were significantly reduced； the content of NO₃^--N, AP, and AK was reduced by 57.7%, 22.0%, and 18.8% compared with that in the control at 3% addition, respectively； and UE activity was inhibited by 13.98%. Further, 16S rRNA sequencing analysis showed that microplastic stress increased the abundance of the Proteobacter group and reduced the abundance of the Acidobacter group in the soil, decreasing the diversity of the community, which in turn destabilized the microbial community and made the entire system less stable. In summary, microplastic stress affects the stability of soybean-soil-microbial systems.