Continuing the series on soil microorganisms, let's talk about the importance of soil rhizobacteria. Rhizobacteria are a type of bacteria that inhabit the soil zone immediately around plant roots as well as the root surface and nodules.
Through a symbiotic relationship with plants, these bacteria enhance and support plant growth and are commonly referred to as plant growth promoting rhizobacteria (PGPR). Through attaching onto the surface of plant roots, these bacteria play a central role in mediating the interactions between roots and soils.
Perhaps the most important function of rhizobacteria in agricultural ecosystems is the conversion of atmospheric nitrogen gas into plant-usable N compounds, such as ammonia, that are available for plant uptake. This process, known as biological nitrogen fixation, is generally performed by rhizobacteria in association with root nodules of N-fixing plants such as legumes.
In this symbiotic relationship between bacteria and higher plants, plant roots form nodules to house the bacteria and provide them with energy sources from photosynthetic sugars that may cost up to 12-25% of the plant's photosynthetic output. In turn, plants can access atmospheric N fixed by bacteria that contributes to increased yield and protein content of seeds.
Rhizobacteria enhance physiological functioning through the release of plant growth promoting substances including phytohormones, antifungal metabolites, and antibiotics.