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Plant functional traits, but not soil abiotic properties, mediate the legacy effects of microplastics on plant community assembly
Summary
Microplastics left behind in soil don't just disappear—they leave a lasting "memory" that reshapes which plants thrive there, favoring grasses over legumes (like beans and peas, which enrich soil naturally). This happens not by changing soil chemistry, but by altering how plants grow and function internally, which could affect food crop diversity and soil health in farmland exposed to plastic pollution. While this study focused on plant communities rather than direct human health effects, it's a reminder that microplastic contamination in soil can have ripple effects on the food-growing ecosystems we depend on.
Soil microplastics (MPs) generate a persistent "memory" shaping the assembly of subsequent plant communities. While the direct effects of MPs have been extensively studied, the underlying pathways governing their legacy effects-whether they operate through altered soil properties (i.e., nutrients and pH) or modified plant traits-remain poorly understood. We examined MP legacy effects on 15 variables across a 12-level MP abundance gradient. Piecewise structural equation modeling (pSEM) was employed to quantify the relative contributions of soil abiotic properties and plant functional traits in mediating MP legacy effects on community assembly. MP legacy significantly increased grass abundance and soil nutrients, but decreased legume abundance. Across the abundance gradient, the majority of the 15 measured variables remained stable, with only the relative electron transport rate (rETR) showing a significant linear decline. pSEM revealed that the community-level shifts were not attributable to the changes in soil nutrients and pH. Rather, MP legacy effects were predominantly mediated via modifications to plant functional traits-specifically rETR, individual plant size, and root/shoot ratio-which emerged as the primary drivers of plant diversity, functional composition, and productivity. Consequently, the footprint of soil MPs on plant communities operates through a trait-mediated filter rather than the modification of soil abiotic properties. By identifying plant functional traits as the key mechanistic link, this study provides a framework for predicting the potential legacy consequences of soil MPs for plant community assembly.