Toxic Impact of Soil Microplastics (PVC) on Two Weeds: Changes in Growth, Phenology and Photosynthesis Efficiency

Experimental evidence on the bio-ecological effects of microplastics on terrestrial plants is still lacking. In this study, we hypothesized that soil polluted with polyvinyl chloride (PVC) microparticles can negatively influence plant traits, photosynthetic efficiency and phenology of two weeds but with different strength in relation to the species’ life traits. Therefore, we conducted an experiment in a common garden growing the wild species Senecio inaequidens and Centaurea cyanus for about 60 days. The possible toxic effects of soil microplastics (1% of PVC in 100 g of soil medium) were investigated, coupling an analyses on plant traits with an evaluation of the microplastic-induced changes in terms of phenology and photosynthetic efficiency. Overall, results showed that plants in control pots were higher and larger than those in treated ones (C. cyanus plant width: p < 0.05; S. inaequidens—plant height: p < 0.05; plant width: p < 0.05). Moreover, for C. cyanus, photosynthetic efficiency (index Fv/Fm) was significantly lower in the treatment than that in control (p < 0.05). About phenology, the second leaf of S. inaequidens emerged earlier in control than that in treatments (day 12.2 ± 0.25 and 14.3 ± 0.3, respectively; p < 0.001). The obtained results highlight that PVC microparticles may have had negative effects on soil–plant system reducing the performance of plants. Since, up to now, research on the interaction between soil microplastics and terrestrial plants has mainly focused on agricultural plants, this work fills a gap of knowledge regarding wild species (weeds), highlighting the possible future impact of microplastics on biodiversity.