Symbiosis: Plants, Nitrogen, and Bacteria

Research Questions:

• What are nitrogen-fixing bacteria?
• What is a symbiotic relationship?
• Do plants have a symbiotic relationship with bacteria?
• What happens when there are no nitrogen fixing bacteria in a growth medium?

Materials:

• Six identical clay pots
• Sphagnum moss or potting soil
• Pea seeds
• Rhizobium leguminosarum inoculant
• Magnifying lens
• Drawing pens and paper
• Marker
• Camera

Experimental Procedure:

1. Label three pots “control” and three pots “bacteria.”
2. Fill all pots with the same amount of moss or potting soil.
3. Follow the manufacturer's recommendations for how to apply the Rhizobium leguminosarum inoculant to nine of the seeds.
4. Plant these nine seeds in the “bacteria” pots. Put three seeds in each pot.
5. Plant the rest of the seeds in the “control” pots. Put three seeds in each pot.
6. Set pots in the sun and water appropriately.
7. Let the peas grow undisturbed for at least nine weeks. During this time, measure the growth of each plant, the number of leaves, and the size of the largest leaves. Note when new leaves form. Take pictures regularly.
8. At the end of nine weeks, pull your plants out of the soil and examine their roots, using a magnifying lens. Draw what you observe.

Terms/Concepts: nitrogen-fixing bacteria

References:

• Nitrogen Fixation, Texas A & M University
• ASM Journals: Symbiotic Nitrogen Fixation and the Challenges to Its Extension to Nonlegumes
• Science of Plant Life: A High School Botany Treating of the Plant and Its Relation to the Environment, by Edgar Nelson Transeau (Nabu Press, 2010)