Chemical trios in rhizosphere ecology: Emerging roles of microbial volatiles, root-derived volatiles, and non-volatile root exudates in plant-soil microbe interactions

The rhizosphere, a narrow zone of soil directly influenced by plant roots, serves as a highly dynamic interface where biochemical and ecological interactions converge to sustain plant growth. This critical region facilitates intricate chemical exchanges among plants, soil, and microorganisms, thereby shaping nutrient availability, microbial community structures, and plant defense mechanisms. While root exudates that are mostly non-volatile have long been the primal interest as ecologically crucial chemicals in the rhizosphere, recent advancements in analytical methodologies have illuminated the roles of volatile organic compounds produced by soil microorganisms (mVOCs) and plant roots (rVOCs) as intricate mediators that regulate plant physiology and microbial community dynamics. mVOCs exhibit diverse functions, including stimulating root development, enhancing systemic resistance, and suppressing pathogen activity, thereby contributing to plant health. Conversely, rVOCs support soil microorganisms in establishing ecological niches in association with plants. mVOCs and rVOCs, together with root exudates, create feedback loops that drive ecological processes in the rhizosphere and enable plants to adapt to environmental challenges. This review synthesizes current understanding in the composition, molecular mechanisms, ecological relevance, and potential applications of mVOCs and rVOCs, with a particular emphasis on their interplay with non-volatile root exudates. The integration of these insights offers a molecular foundation for advancing sustainable agricultural practices and tackling pressing global challenges, such as ensuring food security and mitigating environmental degradation exacerbated by climate change.