[Effects of Biochar Application on Physicochemical Properties and Bacterial Communities of Microplastic-contaminated...

Microplastics are widely distributed in the soil environment, threatening the soil ecological environment system and changing soil physicochemical properties and microbial characteristics. Biochar is often used as a soil amendment to improve soil quality due to its special pore structure and good soil nutrient retention ability. However, the understanding of the effects and mechanisms of biochar application on the physicochemical properties and bacterial communities of microplastic-contaminated soils is still very limited. Therefore, a 21-day micro-soil culture experiment was conducted to analyze the effects of biochar application on physicochemical properties and bacterial community changes in soil contaminated with different concentrations of microplastics using 16S rRNA high-throughput sequencing technology. The results revealed that the application of biochar slowed down the decrease in nitrate nitrogen and Olsen-P contents in microplastic-contaminated soil and increased the total phosphorus content. Biochar addition increased the relative abundance of tolerant phylum such as Acidobacteriota, Actinobacteriota, and Bacteroidota in microplastic-contaminated calcareous soil. Proteobacteria, Acidobacteriota, and Actinobacteriota were the dominant bacteria of the soil bacterial community in each treatment on day 7 and day 21. Compared with that on day 7, the relative abundance of Proteobacteria and Firmicutes significantly decreased, and the relative abundance of Acidobacteriota, Actinobacteriota, Bacteroidota, Chloroflexi, and Myxococcota increased on day 21. Biochar application also increased the relative abundance of Lysobacter in microplastic-contaminated soils. This study demonstrated that the application of biochar increased microplastic-resistant bacteria, enhanced the stability of microplastic-contaminated soil, and slowed down the pollution of microplastics to the soil. Moreover, biochar had great potential to improve the quality of microplastic-contaminated calcareous soil.