According to the NCERT text, fungi form symbiotic associations with plants known as mycorrhiza. Many members of the genus Glomus form mycorrhiza. The fungal symbiont in these associations absorbs phosphorus from the soil and passes it to the plant. Azotobacter is a free-living nitrogen-fixing bacterium, Trichoderma is a free-living fungus used as a biocontrol agent, and Aspergillus is used for producing citric acid.