Deciphering the effects of long-term exposure to conventional and biodegradable microplastics on the soil microbiome

Despite recent advances in the understanding of the impacts of microplastics (MPs) on the soil microbiome under short-term exposure, little information is known regarding the long-term ecological effects of MPs in soil, especially biodegradable MPs (BMPs). Here, we systematically compared the effects of four prevalent microplastics, including two conventional MPs (CMPs) and two BMPs, on the soil microbiome over short- and longterm exposure durations. The soil microbial community were not significantly affected by the MP addition under short-term exposure; however, the soil microbial composition was obviously impacted by MP exposure under long-term exposure, some MP-adapted microbes (e.g., the phyla Protobacteria and Actinobacteria) were enriched but the phyla Acidobacteriota declined. These results indicated that the effects of the MP exposure on the soil microbiome were time dependent. PERMANOVA analysis demonstrated that the exposure time played a more important role in the variation in soil microbiome than the polymer type. The soil microbes which were reshaped by MPs were specialized in genetic potential of lipid metabolism and xenobiotics degradation and metabolism and weakened in microbial genetic information process. The carbon metabolic capacity and nitrogen transformation of soil microbes were disturbed by MPs under long-term exposure. Compared with CMPs, many more MPs derivatives, such as dissolved organic matter and low molecular-weight oligomers, were released from BMPs during the long-term degradation process in soil; thus, BMPs had a stronger effect on the soil microbiome than CMPs under long-term exposure. This study underscores the potential risk of the replacement of conventional plastics with biodegradable plastics.