Microbial diversity loss constrains plastic degradation in marine sediments

Biodegradable plastics are key for ecosystem sustainability relying on microorganisms for their degradation. Unfortunately, microbial diversity is highly vulnerable to global change. Here, applying the dilution-to-extinction approach, we evaluated the impact of loss of microbial diversity on the degradation of five plastics with varying biodegradability under contrasting nutrient regimes in marine sediments in a six-month laboratory experiment. We found that reductions in microbial richness can reduce by up to half the capacity of marine sediments to degrade biodegradable plastics under oligotrophic conditions, with stronger effects observed for highly degradable materials and a gradual decline in degradation efficiency with decreasing microbial richness. Nutrient enrichment partially mitigated the negative effects of diversity loss at low microbial richness. Preserving microbial diversity is thus essential to maintain ecosystem functions and ensure the long-term sustainability of biodegradable plastics under global change.