The unique rhizosphere of aerial roots

This study challenges the conventional definition of the rhizosphere by introducing the concept of the "aerial rhizosphere", which extends beyond underground roots to encompass the mucilage microenvironment surrounding aerial roots. Through a comprehensive comparative analysis of thickness, components, physico-chemical properties, microbiota, and functions, it becomes evident that the aerial root mucilage microenvironment is a dynamic and unique niche, parallel to the conventional rhizosphere. The spatial similarity in thickness implies that both environments offer distinct yet comparable niches for microbial colonization and activity. Despite variations in components and properties, both the rhizosphere and the aerial root mucilage microenvironment play pivotal roles in shaping microbial communities and influencing plant-microbe interactions. The enrichment of nitrogen-fixing bacteria in the aerial root mucilage microenvironment underscores its uniqueness, driven by properties like low oxygen levels and high carbon content. The biofilm-like and protective nature of mucilage creates an ideal habitat for nitrogen-fixing bacteria, demonstrating its dynamic role in fostering specialized microbiota. The mucilage composition, enriched with sugars and endogenous glycosyl hydrolase enzymes, serves as an energy source for resident microbiota, facilitating a complex web of interactions for nitrogen fixation. The symbiotic relationship between plants and nitrogen-fixing bacteria in the aerial root mucilage microenvironment is underscored by the dynamic exchange of carbon and nitrogen, a fundamental aspect of this ecological partnership. As we explore the aerial realm of plant-microbe interactions, this study offers a transformative lens, expanding our understanding of microbial niches and the complex dynamics that govern aboveground roots and ecosystems.