Ecosystem functions of freshwater biofilms: Progress and prospects

Freshwater biofilms are ubiquitous in freshwater environments and are a common way of life for microorganisms in aquatic environments. Although their impacts on ecosystem function and ecosystem services are well documented, little is known about how the species composition of biofilms works together to determine biofilm function. This review summarizes the ecosystem functions of freshwater biofilms. It discusses the roles that freshwater biofilms play in aquatic ecological processes and the adaptations in response to changes in the environment. Freshwater biofilms alter nutrient pathways through their metabolism, contribute to water purification by taking up and transforming aqueous compounds, and utilize extracellular polymeric substances that provide habitat for microorganisms. In addition, hydrological flow rates shape biofilm morphology, nutrient-limited conditions drive changes in biofilm community composition, and biofilm adaptations under light-limited conditions and during short thermal events lead to high stability. Yet, there are still knowledge gaps in our knowledge of the relationship between biofilm ecosystem function and biodiversity. The molecular mechanisms of biofilm function, combined with high temporal resolution monitoring, are future research directions to fill these knowledge gaps. • Research on freshwater biofilm ecosystem functions has deepened and broadened. • Research on biofilm biodiversity and ecosystem function relationships has intensified. • Advanced technologies should clarify biofilm mechanisms. • The impacts of multiple stressors and short-term extreme events on biofilms need attention.