Studying the plant-rhizobia mutualism in the classroom – a guided inquiry activity

Outline

• Brief background– Scientific methods– Study system

• Designing your experiment– Control– Replication– Randomization

Observation

Background Research

Hypothesis/Predictions

Experiment

Data analysis

Not consistent with hypothesis

Consistent with

hypothesis

Scientific Methods

Question

Conclusion

Answer?

Soybean

Rhizobia

CO2+H2O +light C6H12O6+O2

N2 NH3

Phot

osyn

thes

is N

itrogen Fixation

What happens when you add

N in the system?

Background

Fertilizer in agriculture

“….addition of N fertilizer can lead to lower production of nodules in legumes (Rubio Arias et al. 1999; Vargas, Mendes &Hungeria 2000) as well as lower N2fixation rates per nodule (Denison & Harter 1995).”

Background

Scientific Questions:

1) How do rhizobia affect plant growth?

2)How does nitrogen fertilization affect plant-rhizobia interaction?

Questions

Hypotheses

Question1: How do rhizobia affect plant growth?

Hypothesis1:Rhizobia increase plant performance

Hypothesis 2: Fertilized plants have fewer nodules than non-fertilized plants.

Question2: How does nitrogen fertilization affect plant-rhizobia interaction?

Predictions

Question1: How do rhizobia affect plant growth?

Hypothesis1:Rhizobia increase plant performance

Hypothesis 2: Fertilized plants have fewer nodules than non-fertilized plants.

Question2: How does nitrogen fertilization affect plant-rhizobia interaction?

Prediction 1: Rhizobia inoculated plants will have greater biomass than non-inoculated plants

Prediction 2: fertilized plants will have fewer nodules than non-fertilized plants.

1) How do rhizobia affect plant growth?How can we test it?

The control and experimental groups must be identical in all relevant ways except for the introduction of a suspected causal agent into the experimental group.

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Control Treatment 1

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Treatment2

Experiment

Experimental Design

• Control• Replication• Randomization

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Replication

Repetition of a experiment to test the validity of its conclusion + +

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Experiment

Randomization

-Assign treatment randomly to an experimental group

-Eliminate researchers’ bias or judgment + +

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Experiment

Prediction

Control Rhiz (+) Nitrogen (+)

Plan

t Size

???

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Plot a prediction graph on your worksheet

Prediction

2) How does nitrogen fertilization affect plant-rhizobia interaction?

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Experiment

Predictions:

N (-) N (+)

Plan

t Size

N (-) N (+)

# N

odul

es

Plot prediction graphs on your worksheet

Predictions

Experimental DesignCombining Experiment 1&2

n = 10

n = 10

n = 10

n = 10

Each group: 4 treatments x 2 rep = 8 samples Class total = 40

Question 1

Question 2

Experiment

After 1 month….

Record: - Plant height (cm)- Number of leaves- Number of nodules- Aboveground biomass- Belowground biomass

3) Plot graphs using the class data