Effects of Microplastics on Growth, Photosynthesis, and Oxidative Stress-Related Traits in Terrestrial Plants: A Global Meta-Analysis

Microplastics (MPs) can affect growth, photosynthetic, and oxidative stress-related traits in plants, but the reported effects vary among studies. However, the roles of plant groups, MP characteristics, soil properties, and exposure conditions have not been systematically compared across these three trait groups. We compiled 2613 paired observations from 100 independent studies and combined meta-analysis with random forest modeling to quantify MP effects on the three trait groups and compare the relative importance of candidate predictors. Overall, MPs increased oxidative stress-related traits by 19.92% and reduced photosynthetic and growth traits by 12.87% and 12.31%, respectively. Plant-group differences were trait-specific, with numerically larger root reductions in monocotyledons, a larger numerical decline in shoot fresh biomass in dicotyledons, and stronger POD and SOD responses in monocotyledons. Higher MP concentrations corresponded to larger reductions in several biomass traits and plant height. The effects of particle size were less consistent. Biodegradability showed limited differences across traits, with a significant difference detected only for H2O2. Temperature was related to trait responses across all three groups and also ranked highly in the random forest analysis. These results improve our understanding of differences in plant responses to MPs and provide a basis for evaluating MP effects across plant groups, MP characteristics, soil properties, and exposure conditions.