The effect of Rhizobium on Plant Growth By: Madeleine Barrios and Roshan Patel

Introduction  Rhizobia are soil bacteria that fix nitrogen after becoming established inside root nodules of legumes. The rhizobia cannot independently fix nitrogen, and requires a plant host. The rhizobia form nodules on roots that can be observed. Rhizobium tend to work best with legumes plants.

Objective  The objective of this experiment is to test whether or not rhizobium has an affect on the growth of mung beans, red clover, and buckwheat. = +

Hypothesis  We think Rhizobium will benefit the growth of mung beans and red clover because they are leguminous plants. We predict that buckwheat growth will not benefit from the addition of Rhizobium because it is not leguminous.

Materials  Twelve 12-ounce Styrofoam cups.  Perlite soil  String for measuring growth  Ruler  12 Petri Dishes  Graduated cylinder for watering plants  Rhizobium

Experimental Design  We will set up an experiment with a control group that is not exposed to rhizobium and then an experimental group that is exposed to rhizobium.  Control:  2 cups of Perlite with 5 seeds of buckwheat per cup.  2 cups of Perlite with 5 seeds of red clover per cup.  2 cups of Perlite with 5 seeds of mung beans per cup.  Variable:  2 cups of Perlite with 5 seeds of buckwheat per cup and Rhizobium.  2 cups of Perlite with 5 seeds of red clover per cup and Rhizobium.  2 cups of Perlite with 5 seeds of mung beans per cup and Rhizobium.

Procedure  We began by first autoclaving the perlite soil so that we could sterilize the soil and make sure there was nothing in the soil that would affect our results.  We then soaked our seeds of mung beans, buckwheat, and red clover in water for 24 hours.  We then prepared the control group by setting up 2 cups of buckwheat, 2 cups of red clover, and 2 cups of mung beans. Each plant had 5 seeds per cup and the control group was kept away from any possible rhizobium contamination.

Procedure (Continued)  In order to add rhizobium to our plants, we measured out the amount of rhizobium needed for the amount of perlite we had and thoroughly mixed the perlite and rhizobium before setting up our cups.  We then prepared the experimental group by setting up 2 cups of buckwheat, 2 cups of red clover, and 2 cups of mung beans. Each plant had 5 seeds per cup and the perlite contained rhizobium.  In each of the cups, holes were poked at the bottom to allow excess water to escape. Under each a cup a Petri dish was placed to collect the excess water.  In order to measure growth, a ruler and a piece or string was used, and each cup would receive 20mL of water.

Observations  During the experiment, the control group Petri dishes contained more excess water than the experimental group. The Rhizobium used more water.  Mung Beans sprouted first, followed by buckwheat, and then red clover sprouted last.  The plants grew toward the source of light.

Data Averages for Plant Data Plant Average Weight in Grams Average Root Length in cm Average Plant (Stem and Leaf) Length in cm Average Number of Nodules Red clover with Rhizobium Red Clover without Rhizobium Buckwheat with Rhizobium Buckwheat without Rhizobium Mung beans with Rhizobium Mung Beans without Rhizobium

Germination Rates Data (Continued)

Rhizobium Nodules This picture is from one of our experimental plants where nodules can be seen.

Results Red Clover

Results Buckwheat

Results Mung Beans

Interpretation  Based on the charts, the experimental group of plants for mung beans and red clover had more growth than the control group.  The experimental buckwheat had about the same amount of growth as the control group.  The germination rates for control and experimental were not affected by the presence of rhizobium.  The averages for all the plants do not necessarily show that rhizobium helps in plant growth.  However the largest plant from each cup as shown in the graphs do support that rhizobium helps in plant growth.

Conclusion  In conclusion, the experiment was a success because we were able to set up a control and experimental group and observe how rhizobium had an effect on the plants.  Based off the charts, it can be concluded that rhizobium benefits leguminous plants such as mung beans and red clover.  The data also showed that Germination was not affected by the presence of Rhizobium.  The averages do not show a significant difference in the experimental and control group, but that is probably due to the lack of time.

Resources  Blackman, Stuart. Rooting out the Cheats:   Nitrogen Fixation and Inoculation of Forage Legumes. M.B. Adjei, K.H. Quesenberry and C.G. Chambliss2   Rhizobium Bacteria 

Acknowledgements