Effects of different particle size microplastics and di-n-butyl phthalate on photosynthesis and quality of spinach

As agricultural technology advances, microplastics (MP), which result from the degradation of widely used plastic products, have gradually accumulated in the soil, raising serious environmental concerns. This study explores the toxic effects of di-n-butyl phthalate (DnBP) on spinach, focusing on various particle sizes and MP concentrations through hydroponic experiments. Experimental results demonstrated that MP/DnBP combined pollution significantly reduced key photosynthetic parameters, including net photosynthetic rate, stomatal conductance, and transpiration rate, compared to treatments with DnBP or MP alone. Additionally, there was an increase in intercellular carbon dioxide concentration, suggesting that the inhibition of photosynthesis was due to non-stomatal factors. Moreover, spinach exposed to combined pollution conditions exhibited a notable decrease in maximum light energy conversion efficiency, electron transfer efficiency, and chlorophyll content. This disruption affected the synthesis of ribulose-1,5-bisphosphate carboxylase. On the other hand, the contents of ascorbic acid and glutathione in spinach roots and leaves increased, indicating the plant’s defense mechanisms were activated in response the toxic effects of MP and DnBP. Despite this, there was a significant reduction in soluble protein and soluble sugar content and a marked increase in nitrite content, reflecting a decline in spinach quality. This decline was attributed to the exacerbation of DnBP’s toxic effects by MP. Overall, MP/DnBP combined pollution reduced the quality of spinach by impairing photosynthesis and sugar metabolism, potentially amplifying ecological risks to crop plants. This study provides insight into the synergistic effects of MP and DnBP on plant health. • Microplastic (MP) aggravated dibutyl phthalate (DnBP)-induced phototoxicity. • MP/DnBP combined pollution enhanced the activation of spinach defense system. • MP/DnBP combined pollution significantly inhibited the expression of genes encoding nitrate decomposition. • Physical clogging of root pores caused by MP reduced the uptake of DnBP in spinach. • DnBP may interact with superoxide dismutase residues.