Others like mycorrhizal fungi produce vast networks of hyphae that essentially function as additional root surface area to mine soil for nutrients they also provide some pathogen protection to the host roots. Once anchored, some bacteria express genes that convert soil and atmospheric molecules into compounds valuable to the plant, such as nitrogen and phosphorous containing compounds. On the microscopic landscape of a root surface, different symbionts use unique methods to infect. Nitrogen is an element ubiquitously found in amino acids, proteins, and many other cellular components its bioavailability is crucial to the growth of a plant. Symbiotic rhizobia form anaerobic nodules on the roots of legumes and express genes for enzymes like nitrogenase to fix nitrogen into bioavailable compounds for their host plants. Triple-bonded diatomic nitrogen, constituting about 78% of our atmosphere, is highly stable and unable to be used by plants. Phytohormone expression by PGPR have also been proposed to promote the growth of roots through improved water and mineral uptake. Plant growth is promoted in a variety of fashions some bacteria synthesize plant growth hormones like indoleacetic acid and other auxins, while others supply the plant with nutrients from the soil. This broad group of soil bacteria colonizes developing plant roots.

Plant growth-promoting rhizobacteria (PGPR) Common genera include Aspergillus, Mucor, Penicillium Trichoderma, Alternaria, and Rhizopus. They are most commonly found in well-aerated and cultivated top soils. AMF symbiosis promotes host plant uptake of nitrogen and phosphorous. AMF species are highly abundant and play a vital role in their ecosystems by promoting plant growth through numerous mechanisms. They also build scaffoldings of hyphal networks surrounding the plant roots they colonize. Used with permission photograph by Half Hill Farm in Woodbury, Tennessee.ĪMF species produce structures like arbuscules and vesicles (sites of nutrient transfer and storage, respectively). Figure 1 Comparison of plant growth with and without mycorrhizal symbiosis.

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