Unraveling the chemical communication of root exudates and allelopathy for sustainable ecology and agriculture.

Root exudates, a complex mixture of organic and inorganic compounds secreted by healthy plant roots, play a central role in belowground chemical interactions, particularly through the phenomenon of allelopathy. These exudates, which include phenolic acids, flavonoids, amino acids, terpenoids, phytohormones, and fatty acids, do more than support nutrient mobilization and microbial associations. They act as allelochemicals that affect the germination, growth, and physiology of neighboring plants. Allelopathy influences key ecological processes such as plant succession, species dominance, and the establishment of invasive species, while also shaping microbial communities and nutrient cycles in the rhizosphere. Major allelopathic mechanisms include interference with photosynthesis, hormonal disruption, and growth suppression caused by certain amino acids, often producing species-specific and concentration-dependent responses. Autotoxicity, in which a plant inhibits its growth, is now understood as a genetically regulated process. Recent studies show that allelopathic interactions are influenced by plant developmental stages, environmental conditions, and associations with microbes such as mycorrhizal fungi and rhizobacteria. These microbial partners alter both the composition and biological effects of root exudates. Beyond suppression, root exudates also serve as signaling molecules that affect root system architecture and spatial behavior in neighboring plants, allowing donor species to gain a competitive edge. In agriculture, allelopathy offers sustainable options for weed control, organic crop production, and soil health improvement. Invasive species often exploit unfamiliar allelochemicals to displace native flora, supporting the novel weapons theory. This review compiles recent advances and calls for integrated research to apply allelopathy for ecofriendly agriculture.