Photoaging-Induced Phytotoxicity of Tire Wear Particles on Tomato (Solanum lycopersicum L.): Evidence from Oxidative Stress, Metabolic Reprogramming, and Microbial Shifts.

Tire wear particles (TWPs) undergo intricate photoaging processes that substantially alter their physicochemical properties and enhance their environmental behavior and ecological effects. However, the combined effects of particle size and exposure concentration of photoaged TWPs on plant growth and rhizosphere microbial communities remain inadequately characterized. In this study, a 30-day tomato cultivation experiment was conducted using UV-aged TWPs of two sizes (100 and 200 μm) applied at two concentrations (0.1% and 1%, w/w). The results revealed distinct size- and concentration-dependent phytotoxicity. The highest concentration of 100 μm TWPs (1%, w/w) induced the most pronounced inhibitory effects, reducing shoot biomass by 77.1% and net assimilation rate by 62.1%, while increasing malondialdehyde (MDA) content by 72%. UV photoaging altered TWP surface morphology, chemical composition, and hydrophilicity, promoting the leaching of heavy metals. Furthermore, UV-aged TWPs disrupted soil nutrient cycling and enzyme activities, triggered extensive metabolic reprogramming in tomatoes, particularly in carbon metabolism and TCA cycle, and reduced rhizosphere bacterial and fungal diversity, shifting microbial communities toward more stress-tolerant taxa. Integrated analyses demonstrated that the phytotoxicity of UV-aged TWPs was linked to oxidative stress, metabolic disturbance, impaired soil function, and microbial community shifts. These findings advance the understanding of UV-aged TWP toxicity and underscore the necessity of incorporating particle size and aging status into environmental risk assessments.