Microplastics disrupt microalgal carbon fixation: Efficiency and underlying mechanisms

Microalgae are ubiquitous in aquatic ecosystems and play a pivotal role in carbon fixation and cycling. Toxicity of microplastics (MPs) on microalgae in aquatic ecosystems has been widely studied, but their influence on carbon fixation capacity of microalgae remains poorly understood. In this study, the influence of polyethylene (PE) and polyvinyl chloride (PVC) MPs on carbon fixation capacity of Chlorella pyrenoidosa was investigated. During 14-day incubation, the maximum inhibition of carbon fixation was 37.0% and 39.25% for PE and PVC MPs at 50 mg/L, respectively. Moreover, MPs resulted in the decrease of dissolved organic matter (DOM) into water by destroying the algae integrity, while the increase of aromaticity and humification of DOM. The PE and PVC exposure resulted in the reduction of chlorophyll content, and the increase of intercellular oxidative stress, as evidenced by the increased production of stress-related biomarkers. Furthermore, a comprehensive transcriptomes analysis revealed that the differentially expressed genes in GO enrichment analysis were mainly membrane, photosynthetic electron transport chain, chloroplast, etc. KEGG enrichment analysis demonstrated that MPs induced the downregulation of genes involved in chlorophyll metabolism and the Calvin cycle. The findings provide valuable insights into the potential environmental impacts of MPs on aquatic carbon cycles.