Above- and below-ground field study on the impacts of conventional and alternative mesoplastics on Hordeum vulgare growth and soil invertebrate communities.

Plastic plays an important role in agriculture, but its use has become a concerning source of pollution. While new (bio)degradable, alternative plastics are being developed and used as mulching films, their ecological impacts, in particular under field conditions, are not well understood. Furthermore, there is a notable lack of knowledge on how plastic pollution affects soil invertebrate communities. Most existing studies primarily focus on microplastics, often neglecting the impacts of mesoplastics. This study therefore compared the separate effects of two conventional (polyethylene and polypropylene) and two alternative (polyethylene containing biodegradable additives and compostable polylactic acid) mesoplastic films on plant performance (biomass, seed yield) and soil mesofaunal assemblages in a field experiment. The mesoplastics were applied at 0.1% (w/w), prior to soil being planted with Hordeum vulgare (spring barley), which was grown to maturity, for 11 weeks. Generally, there were no measurable differences between the conventional and alternative plastic treatments, however, barley exposed to mesoplastics showed reduced biomass, seed yield, and chlorophyll content, along with increased oxidative stress. Soil fauna, particularly Collembola, had lower richness and abundance when exposed to both plastic types, but assemblage structure and composition remained unchanged after 11 weeks. This study is pivotal in highlighting that both conventional and alternative plastics can similarly affect plant health and soil ecosystems. The evidence provided is essential for refining future risk assessments of agricultural plastic pollution and underscores the urgent need for more sustainable practices and materials in agriculture.