New Insights Into Epiphytic Biofilm Formation, Composition, and Their Role in Submerged Macrophyte Decline Under Environmental Pollution.

Over evolutionary time, submerged macrophytes and their epiphytic biofilms have developed complex interactions, particularly mutualistic interactions. However, environmental pollution can alter biofilms, potentially shifting their influence from supportive to neutral or even inhibitory. This change may be one of the significant driving factors for the decline of submerged macrophytes, yet a systematic review of this phenomenon is still lacking. To this end, we examine the formation and composition of epiphytic biofilms, summarize their effects on submerged macrophyte growth in freshwater lakes, and discuss how they mediate plant changes under increasing exposure to environmental pollution. Epiphytic biofilms, composed of complex biotic and abiotic components, influence submerged macrophytes by modifying light conditions and gas exchange, modulating nutrient competition and antioxidant responses, and releasing allelopathic substances; the magnitude of these effects varies with the biofilm's composition. Environmental pollution might favor resistant or fast-growing species that better compete for nutrients, impair light capture and gas exchange, and release harmful allelopathic substances. This diminishes the beneficial effects of epiphytic biofilms on submerged macrophytes, sometimes even resulting in detrimental impacts. This review examines how environmental pollution alters epiphytic biofilm composition and influences submerged macrophyte communities, providing novel insights into the dynamics of submerged macrophyte communities.