This summary from a leading scientific journal broadly addresses beneficial soil microbes:[1]
The important role of nitrogen fixation by rhizobia and other bacteria for plant growth has been known for decades. What is less appreciated, and less well understood, is the pervasive influence that other microbes have on plant health and growth; they enhance stress tolerance, provide disease resistance, aid nutrient availability and uptake, and promote biodiversity.
…The most intense interactions between microbes and plants take place at the rhizosphere, which is the interface between plant roots and the soil. …Soil microbes have a tremendous influence on plant health and productivity.[2] One straightforward and visible benefit for the plant is a better supply of and access to nutrients. …Arbuscular mycorrhizal fungi, which form an intricate internal symbiosis with the roots of most flowering plants, are associated with the provision of phosphorous to the plant.[3] …Bacteria of the Azospirillum genus promote increased root mass and more efficient nitrogen uptake from the soil in response to the plant hormone indole-3-acetic acid. Using these bacteria and fungi could provide significant environmental benefits as they would allow a reduction in the application of nitrogen and phosphorous fertilizers.
In addition to enhancing the nutrient supply to plants, microbes also confer a degree of protection against plant diseases. In particular, various bacteria and fungi – especially of the genera Pseudomonas, Bacillus and Trichoderma – produce a range of metabolites against other phytopathogenic fungi.2,[4],[5] …With development, such microbes could become a realistic alternative to the heavy fungicide regimens used in agriculture at present. A reduction in the use of these chemicals would lead to obvious environmental benefits….
In addition to these direct effects on plant growth, rhizobacteria exert another health-promoting effect on the plants with which they interact. This phenomena is known as induced systemic resistance and arises when interactions with non-pathogenic bacteria confer better disease resistance on plants.[6]
In summary, the literature shows that beneficial microbes can enhance plant health and growth, and reduce the need for costly fertilizers and chemicals that harm the environment.
[1] Morissey, John P., J. Maxwell Dow, G. Louise Mark, and Fergal O’Gara. “Are microbes at the root of a solution to world food production?” European Molecular Biology Organization’s EMBO Reports: October 2004, 5(10): pp. 922-926) at http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1299160
[2] Bloemberg GV, Lugtenberg BJ (2001) Molecular basis of plant growth promotion and biocontrol by rhizobacteria. Curr Opin Plant Biol 4: 343–350 [PubMed].
[3] Smith SE, Read DJ (1997) Mycorrhizal Symbiosis 2nd ed. San Diego, CA, USA: Academic.
[4] Walsh UF, Morrissey JP, O’Gara F (2001) Pseudomonas for biocontrol of phytopathogens: from functional genomics to commercial exploitation. Curr Opin Biotechnol 12: 289–295 [PubMed].
