Tire wear particles (TWPs) induced toxicity in wheat (Triticum aestivum L.) by affecting osmotic regulation, redox homeostasis, photosynthesis, and microbial density

Tire wear particles (TWPs) are commonly found in soil environments; however, their impacts on soil ecosystems, particularly on wheat (Triticum aestivum L.) physiology, remain largely unexplored. This study aimed to investigate the effects of TWPs at concentrations of T0 (control), T1 (0.05 % w/w), T2 (0.5 % w/w), and T3 (5.0 % w/w) on wheat growth, redox homeostasis, photosynthesis, and soil microbial diversity in contaminated soils. Results revealed that at 5.0 % TWPs, plant height, root surface area, root volume, root length, fresh leaf weight, 100-grain weight, and dry biomass decreased significantly by 22.6 %, 81.4 %, 76.0 %, 73.4 %, 85.6 %, 36.1 %, and 63.1 %, respectively, compared to T0 (p < 0.05). These significant reductions in wheat growth parameters under high TWP concentrations suggest a potential decrease in crop yield and food security. Similarly, malondialdehyde (MDA) levels, indicative of oxidative damage, surged by 66.4 % (leaves) and 68.3 % (roots) under T3 treatment. Antioxidant enzyme activities in leaves increased markedly: ascorbate peroxidase (APX, +162.9 %), catalase (CAT, +132.6 %), dehydroascorbate reductase (DHAR, +112.8 %), and peroxidase (POX, +124.5 %), while glutathione reductase (GR) activity declined by 52.5 %. They also reduced the wheat stomatal conductance and net photosynthetic rate by 28.4 % and 37.0 %, while intercellular CO₂ concentration increased by 8.7 %. Higher concentrations of TWPs influenced the soil microbial diversity, as the average relative abundance of Mortierella showed a stepwise increase, while Plectosphaerella exhibited a gradual decline. In contrast, Tausonia, Gibellulopsis, Schizothecium, Fusarium, Solicoccozyma, Chaetomium, Pseudombrophila, and Gibberella showed a trend of decline with increased concentration of TWPs (p < 0.05). This study demonstrates the ecological toxicity of TWPs, highlighting their adverse effects on wheat physiology and soil microbial communities, and suggests the need for further research on their long-term environmental impact.