SREL Reprint #2833

Root exudates and microorganisms

B-J Koo1, D. C. Adriano1, N. S. Bolan2, and C. D. Barton3

1University of Georgia, Aiken, SC, USA
2Massey University, Palmerston North, New Zealand
3University of Kentucky, Lexington, KY, USA

Introduction: Plant roots influence the physical, chemical, and biological conditions of the soil in the rhizosphere. The biogeochemical reactions induced by microorganisms at the soil-root interface (i.e., rhizosphere) play an important role in the bioavailability of nutrients and metals to plants. This microenvironment is characterized by distinct physical, chemical, and biological conditions compared with the bulk soil, largely created by the plant roots and its microbial associations. Such associations can include nonsymbiotic and symbiotic organisms such as bacteria and mycorrhizal fungi. The microbial populations are an essential part of the rhizosphere and affect the rhizosphere soil by their various activities such as water and nutrient uptake, exudation, and biological transformations.
Organic acids, sugars, amino acids, lipids, coumarins, flavonoids, proteins, enzymes, aliphatics, and aromatics are examples of the primary substances found within this microzone. Among them, the organic acids have received considerable attention owing to their role in providing substrates for microbial metabolism and for serving as intermediates for biogeochemical reactions in soil.
Nutrients and metals are typically present in the soil solution at low concentrations and tend to form sparingly soluble minerals (except nitrogen, sulfur, and boron), or may be adsorbed to a solid phase through ion exchange, hydrogen bonding, or complexation. The extent to which they are transferred from the soil to the biota (i.e., microbes or plants) is dependent on the biogeochemical interactions and/or processes among the soil, plant roots, and microorganisms in the rhizosphere. At this interface, the presence of root exudates may influence chemical reaction kinetics within the soil environment and subsequently affect biological activities. As such, understanding the role of the rhizosphere on biogeochemical processes within the soil is essential for developing bioremediation technologies of inorganic and organic contaminants.

SREL Reprint #2833

Koo, B-J, D. C. Adriano, N. S. Bolan, and C. D. Barton. 2005. Root exudates and microorganisms. pp. 421-428 In D. Hillel (Ed.). Encyclopedia of Soils in the Environment. Elsevier Academic Press. Amsterdam, The Netherlands.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).