Phytostimulation is the process where root released compounds enhance microbial activity in the rhizosphere. This process is critical for the applied technology of rhizoremediation that combines phytoremediation and bioaugmentation. This type of rhizosphere phytoremediation can be used as a low-cost approach to remove organic pollutants from the soil.
Phytostimulation is important for rhizoremediation for multiple reasons. First, the rhizosphere provides a specific niche for soil microorganisms to live. This niche is continuously expanding as roots grow and penetrate new soil zones. Root exudates provide many benefits for microorganism growth and activity. Root released compounds have many roles in phytostimulation because they often mimic man-made pollutants. The rhizosphere serves as a unique soil habitat, full of organic compounds that may serve as energy sources for microorganisms. Alternatively, these organic compounds may serve as inducers for microbial genes involved in degradation, or as co-metabolites that are necessary for pollutant degradation to occur. A classic example of a plant secondary metabolite that can induce a bacterial enzyme important for PAH degradation is salicylate, which induces naphthalene oxygenase in Pseudomonas.
Another aspect of phytostimulation is the cultivation of new microorganisms in the soil. Because of the distinct rhizosphere habitat that is produced by living plants, microorganisms may be inoculated on plant seed to introduce specific organisms to the growing rhizosphere. Inoculated organisms may be genetically engineered or naturally occuring strains that perform a specifc function of interest for remediation.