The hidden constrains in soil ecology and plant physiology: microplastic effects on nutrient and metal transport in soil-plant continuum

Background: Plastic pollution, particularly microplastics (MPs), is a growing ecological concern. In agroecosystems, plastic mulches enhance crop production but, alter nutrient cycles, affect soil structure and aeration, and may disrupt to soil-plant interactions and human health. Aim: The research, through a multifaceted and ecological approach, aimed to investigate: i) the interaction between microplastics and element translocation from soil to plants; ii) plant morphological, biochemical, and physiological responses to MPs-contaminated soils; iii) differential effects of conventional (PE) and biodegradable (BPs) MPs on soil and plants. Methods: Lettuce was grown in soils amended with 1% and 2% PE or BPs. At harvest, soil properties, nutrient status, heavy metals concentrations were analysed. Plant biometry, photosynthesis, bioaccumulation, translocation, and metal transporter gene expression were evaluated. Untreated soils served as controls. Results: The addition of 2% of PE and BP significantly (p < 0.001) reduced soil nutrients: nitrate (−7.5%; −15.5%), nitrite (−65.4%; −46.5%), and sulphate (−13.9%; −31%, respectively). In 2%BPs treated-leaves, Zn (−96%), K (−39%), and Mg (−33%) significantly (p < 0.001) decreased as well as in plant growth (−67%) and photosynthesis (−24%) were reduced. Metal-transporter expression was significantly (p < 0.05) upregulated in 2%PE-treated roots (NRAMP5:+21.4, ZIP:+7.74, IRT1:+2.21, HMA3:+2.64) and leaves (IRT1:+3.2-fold), and 2%BPs-treated roots showed NRAMP5 (+18.2), ZIP (+5.81), and IRT1 (+2.13) upregulation. Conclusion: BPs constrained plant growth and both MPs types triggered a molecular response. MPs’ presence in soils can be considered a stressor for plants as the consequent changes in element availability in soils caused alterations of bioaccumulation and translocation indices and upregulation of metal transporter genes.