ABSTRACT
The belowground parts, roots in vascular plants and rhizoids in bryophytes, play critical roles for adaptations and productivity of land plants. The rhizosphere, which is the narrow region of soil that surrounds roots/rhizoids, is enormously rich in nonplant species. How roots/rhizoids interact with such diverse soil organisms remains largely uncharacterized. Nonetheless, some constituents of root exudates, which are metabolites that are produced by roots and rhizoids and secreted into the rhizosphere, have been demonstrated to impact root-soil organism interactions. Germane to this chapter, there is increasing evidence that volatile organic compounds, a subset of root metabolites, play important roles in mediating diverse types of interactions between roots and other soil organisms. This chapter discusses four types of such belowground interactions: (1) volatile-mediated belowground plant–plant interactions; (2) volatile-mediated belowground plant–insect interactions; (3) root-beneficial microbe interactions mediated by volatiles, and (4) plant defense against microbial pathogens mediated by volatiles.
