Microplastics significantly impact soil biophysical properties, affecting soil structure, water holding capacity, and microbial function. A 5-week garden experiment exposed loamy sand soil to four common microplastic types (polyacrylic fibers, polyamide beads, polyester fibers, and polyethylene fragments) at environmentally relevant concentrations (up to 2%). The study measured bulk density, water holding capacity, hydraulic conductivity, soil aggregation, and microbial activity. Microplastics altered bulk density, water holding capacity, and the relationship between microbial activity and water-stable aggregates. These effects are underestimated if particle type and concentration variations are ignored, suggesting that qualitative microplastic data may not be sufficient for assessing soil impacts. Microplastics, due to their persistence and non-natural properties, may act as drivers of environmental change. The study highlights the need to understand how microplastics affect the natural relationships between soil particles and biota. The results show that microplastics can significantly alter soil biophysical properties, with polyester fibers causing the most noticeable changes. These changes may affect soil structure, water retention, and microbial activity, potentially leading to long-term environmental consequences. The study also discusses the nonmonotonic responses observed in some soil biophysical proxies, indicating that microplastic effects may not follow a simple concentration-dependent pattern. This complexity underscores the importance of considering multiple factors, including particle type, size, and polymer composition, when assessing microplastic impacts. The findings suggest that microplastics could be significant long-term anthropogenic stressors in terrestrial ecosystems, influencing global change processes. Further research is needed to fully understand the mechanisms behind these effects and to assess their broader environmental implications.Microplastics significantly impact soil biophysical properties, affecting soil structure, water holding capacity, and microbial function. A 5-week garden experiment exposed loamy sand soil to four common microplastic types (polyacrylic fibers, polyamide beads, polyester fibers, and polyethylene fragments) at environmentally relevant concentrations (up to 2%). The study measured bulk density, water holding capacity, hydraulic conductivity, soil aggregation, and microbial activity. Microplastics altered bulk density, water holding capacity, and the relationship between microbial activity and water-stable aggregates. These effects are underestimated if particle type and concentration variations are ignored, suggesting that qualitative microplastic data may not be sufficient for assessing soil impacts. Microplastics, due to their persistence and non-natural properties, may act as drivers of environmental change. The study highlights the need to understand how microplastics affect the natural relationships between soil particles and biota. The results show that microplastics can significantly alter soil biophysical properties, with polyester fibers causing the most noticeable changes. These changes may affect soil structure, water retention, and microbial activity, potentially leading to long-term environmental consequences. The study also discusses the nonmonotonic responses observed in some soil biophysical proxies, indicating that microplastic effects may not follow a simple concentration-dependent pattern. This complexity underscores the importance of considering multiple factors, including particle type, size, and polymer composition, when assessing microplastic impacts. The findings suggest that microplastics could be significant long-term anthropogenic stressors in terrestrial ecosystems, influencing global change processes. Further research is needed to fully understand the mechanisms behind these effects and to assess their broader environmental implications.