Microplastics reduce the wheat (Triticum aestivum L.) net photosynthetic rate through rhizospheric effects

Microplastic accumulation after film mulching affects nutrients cycling in the soil–crop system. Bulk soil (BS) and rhizosphere soil (RS) have two different community compositions which lead to their different microbial nutrient acquisition abilities. Microplastics influence the rhizosphere effect. However, the mechanism by which microplastic accumulation affects the net photosynthetic rate (NPR) through rhizospheric microbial communities remains unknown. This study aimed to identify the mechanisms underlying the effects of polyethylene (PE) and polyvinyl chloride (PVC) microplastics at 0, 1, and 5% (w/w) on the NPR in the wheat–soil ecosystem using a pot experiment. Superoxide dismutase (SOD) activity was reduced by 15.35–36.7%, and that of peroxidase (POD) was increased by 32.47–61.93%, causing reductions in NPR (17.94–23.81%) in the PE5% and PVC (1 and 5%) (w/w) treatments compared with the control. The Chao1, Shannon, and Simpson indices of the bacterial and fungal diversities were lower in BS than in RS at PE1% and PVC5% (w/w), respectively. The bacterial and fungal network complexities were reduced and increased, respectively, owing to alterations in the bacterial and fungal community compositions and structures for wheat growth. The Mantel test showed that the bacterial and fungal diversity indices in BS had positive correlations with Olsen-P and phosphatase; however, those in RS were positively correlated with NO₃^– and β-1,4-glucosidase. The structural equation model indicated that wheat enzymatic and soil hydrolytic activities negatively affected NPR. Wheat has a profound antioxidant defense strategy for PE and PVC microplastic stress, which produces a synergistic effect of POD by protecting organelles and reducing tissue damage to preserve the NPR.