Temporal succession outweighs substrate characteristics in shaping riverine plastisphere biofilm on textiles

Biofilms developing on plastic surfaces (the plastisphere) are increasingly recognized for their ecological significance, yet the drivers of community biomass and biodiversity remain poorly understood. Moreover, plastisphere research has focused on a narrow range of polymers, leaving widely distributed substrates such as textiles understudied. Here, we assessed the relative importance of temporal succession and substrate properties (polymeric composition and color) in shaping microalgal and bacterial community composition and photosynthetic abundances, and evaluated whether substrate-specific selection results in long-term community divergence or is restricted to early colonization. We conducted a mesocosm experiment simulating a lotic system to examine biofilm development on polyester textiles and non-synthetic analogue (cotton), each in two colors (black, white). Prokaryotic and microalgal eukaryotic community composition (16S, 18S rRNA), together with pico-photosynthetic abundances assessed by flow cytometry, were monitored over five time points spanning 7 to 35 days. Microbial diversity, community composition, and inferred prokaryotic functions did not differ significantly among polymer types or colors, indicating that substrate characteristics played a limited role in overall community assembly and the predominance of opportunistic colonization, despite the presence of indicator species. In contrast, microalgal abundances differed among substrates, with higher abundances observed on cotton, suggesting that substrate properties may still influence specific aspects of biofilm development. Temporal succession emerged as the primary driver of community change, with significant effects observed for prokaryotic communities even over short timescales. These findings emphasize that temporal dynamics must be explicitly considered in plastisphere studies, as differences in colonization time may confound interpretations of substrate effects.