An Exploration of Composition and Roles of Root Exudates in Controlled Environment Agriculture: Impacts, Functions, and Case Studies—A Systematic Review

Two decades of research has revealed an intricate network of root exudates in plants, which they use to interact with and mediate their surrounding environment, the rhizosphere. Prior research has been conducted mainly on model plants such as Arabidopsis or staple monoculture crops like maize, soybean, and rice, revealing crucial roles in plant growth, microbiota interaction, and nutrient acquisition. However, similar research has only begun to be conducted in Controlled Environment Agriculture (CEA) systems. This review synthesizes the existing literature to examine the composition, functions, and influences of vegetable root exudates within CEA systems. The first section explores key compounds (including amino and organic acids, and sugars) along with mechanistic processes, and microbial interactions. The second section compares root exudates in soil-based versus hydroponic CEA systems based upon differences in substrate, (a)biotic stressors, microorganisms, and nutrient availability. The final section presents case studies where root exudates have aided in environmental stress mitigation, allelopathy, disease response, and pest control. Lastly, we ponder the future avenues of exploration for CEA root exudates, proposing the creation of a database for usage in smaller or organic farms. In conjunction, we emphasize the need for further investigation into the potential of exogenous applications of exudate-like compounds to positively impact yield, disease resistance, soil restoration, and land reclamation, especially in the context of climate change.