Assessing the impact of nanoplastic and microbial interactions on the physiology of zea mays

Polystyrene nanoplastics (PSNPs) are emerging contaminants in agroecosystems, introduced primarily through sludge application and mulching. Their interactions with soil microbiota and subsequent effects on crop physiology remain poorly understood. This study examined maize physiological responses to PSNP (<100 nm) exposure and evaluated the potential of Pseudomonas chlororaphis RP4, a strain with esterase and lipase activity, to influence plant performance under such stress. Five-day-old seedlings, germinated on water-agar, were transferred to full-strength Hoagland solution with PSNPs (1 and 10 mg/L) and bacterial inoculum, and grown hydroponically for 14 days under controlled conditions (28 °C day/22 °C night; 16/8 h light/dark). PSNPs induced concentration-dependent growth inhibition: while 1 mg/L had minimal impact, 10 mg/L significantly reduced shoot length and fresh weight (p < 0.05). This significant adverse effect on shoot growth at 10 mg/L was accompanied by a reduced root biomass (p < 0.05). At 1 mg/L, bacterial inoculation had no significant effect relative to PSNP-alone treatment (p > 0.05). Root morphological traits (length, surface area, diameter) and chlorophyll content did not differ significantly across treatments, though minor, non-significant trends suggested dose-dependent variation. Bacterial viability (OD600) varied with PSNP concentration and plant presence, declining in maize-associated treatments (p < 0.05) but increasing in axenic cultures (p > 0.05). Total biomass and shoot-to-root ratios remained statistically unchanged (p > 0.05). The study provides an evaluation of plant-nanoplastic-microbe interactions, showing that RP4 can partially mitigate PSNP-induced phytotoxicity in a dose-dependent and context-specific manner. These findings provide mechanistic insight into how PSNPs influence maize physiology and root-associated microbial interactions under strictly controlled conditions, establishing a basis for future investigation in soil systems.