Biochar mitigates micro- and nano-plastics stress in Arabidopsis thaliana L. by modulating plant physiological responses and improving soil chemical and biochemical conditions

The accumulation of micro- and nano-plastics (MNPs) in terrestrial ecosystems poses an emerging threat to soil health and plant development. This study examined the effects of fluorescent polystyrene MNPs (0.1-100 & micro;m; 0.01-1 g L- 1) with heterogeneous sizes and shapes on soil properties, microbial activity, and the morphophysiological traits of Arabidopsis thaliana. In parallel, we assessed whether biochar (20% v/v) could mitigate MNPs-induced alterations. MNPs contamination decreased the soil cation exchange capacity and modified micronutrient availability without affecting pH, whereas biochar significantly increased pH, carbon, and nutrient content. In control soils, higher MNPs concentrations delayed germination and reduced shoot biomass and rosette area, while biochar-amended soils maintained stable or enhanced plant growth and root development across all contamination levels. MNPs exposure induced oxidative stress in roots, with increased hydrogen peroxide and superoxide radical accumulation, but did not upregulate the expression of three root peroxidase genes. Biochar improved microbial biomass and basal respiration, although its combination with MNPs resulted in complex and enzyme-specific responses. Overall, biochar ameliorated several adverse effects of MNPs contamination by enhancing soil fertility and plant performance, suggesting its potential as a sustainable soil amendment to mitigate plastic pollution in terrestrial environments.