Plastic pollution is widely recognized as a pervasive global issue affecting ecosystems worldwide, including freshwater environments. Its impacts extend across multiple ecological dimensions and can reverberate through key ecosystem functions. One important pathway is the alteration of biogeochemical cycles, particularly the carbon cycle, via effects on aquatic metabolism, which governs the production and consumption of organic matter in aquatic systems. This process is driven by multiple mechanisms, including the formation of biofilms on plastic surfaces (the “plastisphere”), which host diverse communities of autotrophic and heterotrophic organisms capable of influencing this metabolic balance. Despite growing attention, coordinated large-scale studies across environmental gradients remain scarce, limiting our understanding of plastisphere biodiversity and its functional implications. Here, we present the framework of a project designed to address these knowledge gaps, along with preliminary results from a globally coordinated experiment. In this experiment, pristine polypropylene and low-density polyethylene were incubated under semi-natural conditions in the subsurface waters of lakes spanning a range of trophic states and latitudes for 30 days, allowing for natural biofilm development. Biofilms were characterized using chlorophyll-a and ash-free dry mass measurements, while microbial community composition was assessed through 16S, 18S rRNA, and ITS metabarcoding. Additionally, short-term incubations were conducted to estimate net ecosystem productivity associated with plastic-colonized biofilms. This framework will allow us to explore how epiplastic communities vary across different polymer types, while disentangling the relative influence of environmental conditions and substrate properties on biofilm development. It also provides an opportunity to assess whether plastisphere formation can drive shifts in ecosystem metabolism toward net autotrophy or heterotrophy. By synthesizing data across diverse freshwater systems, this study seeks to advance our understanding of plastics as novel ecological substrates and to clarify their role in shaping biogeochemical processes at a global scale.