Conventional and biodegradable agricultural microplastics affect soil properties and microbial functions across a European pedoclimatic gradient

Agricultural plastics (AP), as a potential source for microplastic (MP) soil contamination, have attracted increasing interest recently. Namely, mulching films with low rates of removal and recycling are important sources of MP generated during their erosion and fragmentation. This study investigates the effects of agricultural MPs from different mulching films: conventional (linear low-density polyethylene, PE) and biodegradable (starch-blended polybutylene adipate co-terephthalate, PB). In 2022, MPs were mixed into soils at experimental fields located in three EU countries representing contrasting pedoclimatic conditions (Finland, Germany, and Spain) using realistic MP concentrations of 0.005% and 0.05% (w/w dry soil). In the two following growing seasons 2022 and 2023, soil physico-chemical properties, aggregation, microbial diversity and functions were studied. Soil properties and microbial community structure showed statistically significant differences between plots contaminated by MPs and controls, although the results were inconsistent. But then again, the microbial activity revealed repetitious decreases in soils contaminated by MPs. The effects were observed for all three countries and both conventional and biodegradable MPs. However, the decreases were more evident after two years of MP contamination and at the higher concentrations of MPs. As the higher MP concentration (i.e., 0.05% w/w) is environmentally relevant in Europe, our findings emphasize the potential harmful effects of microplastics from agricultural plastics on soil health. Further, the effects increased in abundance from north to south, revealing the importance of considering the pedoclimatic conditions and highlight concerns about their impact on sustainable agriculture in different European regions.