Abstract

Microplastics (MPs) alter soil properties and plant physiology and pose a significant risk to crop health and food quality. This study assessed the effects of MPs (polyamide-PA, low-density polyethylene-LDPE, and polypropylene-PP) on Andisol and Raphanus sativus L. as a model plant. Plant characteristics, including growth, chlorophyll content, oxidative stress, antioxidant capacity, and bioactive compound profiles, were evaluated. In addition, the effects on soil nutrients, microbiological properties, and bacterial nitrogen-cycling gene abundance were studied, revealing alterations in both soil and plants. Soil pH increased up to 4.3%, whereas dissolved organic carbon and polyphenol levels decreased, particularly in the PA (26%) and PP (29%) treatments. LDPE and PP increased beta-glucosidase activity (14% and 23%, respectively) and basal soil respiration (25% and 26%, respectively). Nitrogen-cycling genes nifH, amoA, and nirS were notably more abundant in PP-treated soils, with increases of 79%, 76%, and 62%, respectively. In R. sativus , PA and LDPE increased SPAD values by 9.9% and increased biomass in rootlets (155% in PA, 60% in LDPE) and radishes (125% in PP). Oxidative stress levels in radishes increased by 63% and 73% after exposure to LDPE and PP, respectively. MPs altered glucosinolate profiles in leaves and rootlets. Furthermore, PA and LDPE modified anthocyanin profiles in leaves, whereas PP altered the profile in radishes. This study highlights the impact of MPs on soil and plant physiology, identifying polyphenols and microbial biomass carbon as key predictors of R. sativus response.