Biochar and silicon oxide nanoparticles ameliorate micro-plastic stress in alfalfa by enhancing photosynthesis, antioxidant defense, phyto-hormones balance and soil quality

The accumulation of microplastics (MPs) in agricultural lands poses serious threats to crop productivity and human health. Biochar (BC) and nanoparticles (NPs) have emerged as front-runners in counteracting abiotic stress. Therefore, this study aimed to explore the role of BC and silicon oxide nano-particles (SiO-NPs) to alleviate MPs toxicity in alfalfa. The study had the following five treatments: control, MPs (1%) contaminated soil, MPs (1%) + BC (2%), MPs (1%) + SiO-NPs (50 mg L-1), and MPs (1%) + BC (2%) + SiO-NPs (50 mg L-1). Microplastics diminished the alfalfa growth and biomass productivity by inhibiting the photosynthetic traits, increasing oxidative damage, decreasing soil nutrient availability, and inducing soil acidity. Results demonstrated that BC + SiO-NPs alleviated MPs toxicity and boosted the alfalfa growth and biomass. Biochar with SiO-NPs enhanced biomass yield by increasing chlorophyll synthesis (60.56-64.12), stomatal conductance (Gs: 53.33), transpiration rate (Pn: 46.78%), inter-cellular carbon dioxide (Ci: 33.57%) and photosynthetic rates (Pn: 42.10%), antioxidants activities (33.58-131.86%), indole acetic (IAA: 72.58%), gibberellin acid (GA: 58.60%), salicylic acid (SA: 34.46%) synthesis and decreasing the hydrogen peroxide (H2O2: 59.85%), malondialdehyde (MDA: 62.68%) and abscisic acid (ABA: 34.64%) synthesis. This study demonstrates that combined BC and SiO-NPs effectively mitigate MPs via improving antioxidant activity, photosynthetic activity, restoring hormonal balances, and soil health. These findings provide insights to develop strategies to improve soil health and crop productivity in MPs contaminated soils.