Biodegradable and Conventional Microplastics Differentially Affect Soil Nutrient Availability and Stress Responses in Spinach (Spinacia Oleracea L.)

The mismanagement of agricultural mulches leads to the production of microplastics (MPs) impacting soil and plants. This research aimed to evaluate the potential alterations in the soil-plant system due to MPs in the soil, focusing on element availability, accumulation, translocation in spinach (Spinacia oleracea L.), and their effects on plant performance. Two types of MPs (bioplastic: B; conventional plastic: P) were added at different rates (0.5, 1, and 2% dry weight) in soils where spinach was grown in 35 mesocosms (5 as control and 5 for each rate of B and P-treatments). Soil samples were analyzed for pH, N, Corg, NH4+, SO42-, elements availability and their fate in spinach roots and leaves. The impact on soil was evaluated through microbial respiration (Resp), DNA yield, and eubacterial and fungal abundances. Spinach performance was assessed by photosynthetic activity, weight, length, leaf relative water content, specific leaf area, chlorophyll and carotenoid contents, and several stress responses (GAE, FRAP, HSP70, APX, GR, CAT). The findings showed only lower Resp in B-treated soils compared to controls. Element availability was significantly higher in 2%-P-treated soils and lower in B-treated soils than in controls. Spinach roots accumulated all investigated elements, but translocation varied per element. Spinach grown in soils with biodegradable MPs had reduced biomass and lower leaf C and N contents, whereas those in soils with conventional MPs exhibited physiological and biochemical alterations, increasing antioxidant activity in leaves. In conclusion, both types of MPs in soil pose a serious risk to plant and soil health.