From Laboratory Simplicity to Ecological Realism: A Conceptual Framework for Interpreting Microplastic Effects on Seed Germination and Early Plant Development

Microplastics are increasingly recognized as contaminants that may affect seed germination and early seedling establishment, yet the ecological significance of these responses under natural soil conditions remains uncertain. Evidence from controlled studies includes reduced germination, altered germination timing and synchrony, and impaired early root development, but responses vary with particle properties, exposure intensity, growth medium, plant species, and exposure duration. Here, we examine how experimental simplification can influence the detection and interpretation of microplastic effects during the earliest stages of plant establishment. We propose “experimental inflation” as a hypothesis-generating framework referring specifically to increased response detectability and apparent consistency that may arise when exposure probability is increased and environmental variability is reduced; it does not imply larger biological effects or greater ecological risk. We distinguish this concept from ecological realism, exposure realism, external validity, signal-to-noise ratio, and statistical power, and we discuss how concentration, substrate heterogeneity, exposure duration, and biological complexity operate through different pathways. We further synthesize representative quantitative evidence and outline a tiered experimental framework in which polymer characteristics, exposure metrics, soil properties, plant species, germination endpoints, and statistical approaches are harmonized across laboratory, realistic soil, mesocosm, and field studies. This framework is intended to generate testable hypotheses rather than establish a universal direction or magnitude of microplastic effects.