Plant Root Exudates

Plant Root Exudates are the organic compounds released by plants into the soil through their roots. Plants release a number of compounds through their roots, including sugars, amino acids, organic acids, hormones, and vitamins.


 * "In annual plant species, 30 to 60% of photosynthetically fixed carbon is translocated to the roots, and a considerable proportion of this carbon (up to 70%) can be released into the rhizosphere... This rhizodeposition is affected by multiple factors such as light, intensitiy, temperature, nutritional status of the plants, activity of retrieval mechanisms, various stress factors, mechanical impedance and sorption characteristics of the growth medium, and microbial activity in the rhizosphere."

Impact on Soil Microbes

 * "The rhizosphere is thus an environment created by the interactions between root exudates and microorganisms, which may either utilize the organic materials, released as nutrient sources or be inhibited by them. The plant-microbe relationship is more often on the former, where microbes take advantage of nutrients provided by the plant. In return, microbes may assist thep lant, for example, by making nutrients available or by producing plant growth-promoting compounds, or may cause harm to it, for example, by acting as plant pathogens. In general, the microbes that inhabit the rhizosphere serve as an intermediary between the plant, which requires soluble inorganic nutrients, and the soil, which contains the necessary nutrients but mostly in complex and inaccessible forms."

Concentrations of microbes in the rhizosphere can reach between 10,000,000,000 and 10,00,000,000,000 cells per gram of rhizosphere soil and "invertebrate numbers in the rhizosphere have been shown to be at least two orders of magnitude greater than in the surrounding soil." The microbes in the rhizosphere are largely supported by exudates from the roots.

Related Sourcewatch

 * Soil Life
 * Synthetic Fertilizer
 * Prokaryotes
 * Mycorrhizal Fungi

External Resources

 * Janice S. Snow, Misunderstanding Soil Ecosystems: How flawed conceptions of soil have lead to flawed U. S. land, water and climate policies, Masters Thesis, Tufts University, November 2009.