Question

In what type of soil would you expect to find plants with an abundance of root nodules? Please explain your answer.

Answer 1

Nitrogen-limiting soils.

When the nitrogen is limiting, capable plants form a symbiotic relationship with a host-specific strain of bacteria, rhizobia. Rhizobium fix atmospheric nitrogen (N2) and is converted into ammonia (NH3), which is then assimilated into amino acids, nuclei acids, and other cellular constituents.

The high nitrogen content in soil blocks nodule development as there is no benefit for the plant of forming the symbiosis.

Nitrogen is the most commonly limiting nutrient in plants and certain plants use nitrogen fixing bacteria, specifically symbiotic rhizobia bacteria, within their root nodules to counter the limitation. When nitrogen is excess in the soil, nitrogen fixation is not necessary. However, plants can directly use nitrogen from the soil without the help of rhizobium bacteria.