From full-scale composting of Organic Fraction of Municipal Solid Waste (OFMSW) with compostable plastic packaging to field application: Effects on wheat growth and rhizosphere microbiome structure

Global efforts toward a circular bioeconomy have promoted compostable plastics (CPs) as sustainable alternatives to petroleum-based materials. CPs can be co-composted with the Organic Fraction of Municipal Solid Waste (OFMSW) to produce compost for agricultural use, potentially reducing reliance on mineral fertilizers. Yet, their impacts on soil microbial dynamics and crop performance remain poorly characterized. In this study, we evaluated the impact of compost (BioP) derived from industrial-scale co-composting of OFMSW and 2.6 % (w/w) CP food packaging (Mater-Bi) on wheat (Triticum aestivum) performance and rhizosphere microbial communities, compared to standard OFMSW compost (Comp). A single field trial (November 2021-July 2022) tested three treatments: no fertilization (Ctrl), Comp, and BioP amendments. Wheat traits were not significantly affected by compost treatments. Compost application, however, influenced the structure and composition of rhizosphere microbial communities, promoting beneficial taxa linked to nutrient cycling and plant health. Both composts promoted carbon-linked metabolisms (e.g., fermentation, > 20 % increase), and metabolisms linked to aromatic compounds degradation (up to a + 193 %). BioP, in particular, enriched several plastic-degrading microorganisms, shaped a distinct microbial network, and harboured unique bacterial (84 genera) l and fungal (35 genera) taxa, including genera known for their role in bioplastic degradation, like Alcanivorax, Cupriavidus, Saccharomonospora, Themomonospora, Amycolatopsis, Emericellopsis, Knufia, and Rhodotorula. Within the limits of a single-season field trial, our results indicate that compostable plastic packaging can be co-composted with OFMSW without adverse short-term effects on compost quality, wheat growth, or rhizosphere microbial communities, supporting its potential as a sustainable alternative to conventional plastics.