High doses of polypropylene and polyvinyl chloride microplastics affect the microbial community and nutrient status of vineyard soils

The escalating use of plastic materials in viticulture causes release of microplastics (MPs) into vineyard soils. This study examines the impact on soil health of polypropylene (PP) raffia and polyvinyl chloride (PVC) tube strings, commonly mulched into the topsoil after use. A 120-d incubation experiment was conducted with soils exposed to high doses (10 g/kg) of microplastics (MPs) from standard, new and used strings. The study investigated alterations in the microbial community, bioavailability of macronutrients (NH4+ and NO3−, P, K, Ca, Mg), and bioavailability of micronutrients (Cu, Zn, Fe, Mg). The presence of MPs significantly stressed the soil microbial community, reducing microbial biomass by 30% after 30 d, with the exception of PVC in acid soil, which caused an unexpected increase of about 60%. The metabolic quotient (qCO2) doubled in MP-polluted soils, with PVC exerting a more pronounced effect than PP. Basal respiration increased by 25% relative to the acid control soil. PVC MPs raised soil pH from 6.2 to 7.2 and firmly reduced the bioavailability of micronutrients, particularly in acidic soils, and led to a 98% reduction in nitrate (NO3−). The availability of NH4+, P, K, Mg decreased by 10% and Cu, Fe, Mn, Zn by 30%. However, Ca availability increased by 30%, despite shifting from the acid-soluble fraction to soil organic matter and crystalline minerals. Calcareous soil was generally more resilient to changes than the acid soil. These findings underscore the urgent need to investigate the long-term effects of MPs from viticulture on soil properties and health. (Figure presented.)