Aerial polyethylene deposition alters strawberry physiology and rhizosphere functionality

Although root-level microplastic (MP) effects on plants and soil are well studied, little is known about aerial MP deposition. We hypothesized that polyethylene (PE) contamination of strawberry shoots reduces plant biomass and photosynthetic parameters, alters elemental composition, and declines microbial abundance and enzymatic activity within the rhizosphere. Strawberries were grown in soil and sprayed with water as a control, 1.25 mg of PE or lignin three times during a 120-day experiment. Importantly, the PE was never in contact with the soil. We measured photosynthetic performance, growth traits, shoot and root elemental composition, as well as rhizosphere microbial abundance and enzymatic activity. Our results only partially confirmed our hypothesis. PE exposure decreased plant height but increased root water content. Both effects are likely linked to the alteration of the photosynthetic apparatus, as intercellular CO 2 , transpiration rate and stomatal conductance were all significantly higher in both treatments, while net photosynthetic rate was decreased in PE only indicating a biochemical limitation caused by PE. PE application increased shoot K and root Mg and Mo content. Finally, we demonstrated for the first time that aerial contamination of PE (also lignin) can indirectly influence rhizosphere enzymatic activity, leading to increased lignin peroxidase activity. In contrast, rhizosphere microbial abundance remained unaffected by both the treatments. Our study provides new evidence that aboveground MP stress can induce physiological modifications that extend belowground, influencing both plant functional traits and rhizosphere dynamics.