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

Outline Brief background Designing your experiment Scientific methods Study system Designing your experiment Control Replication Randomization

Not consistent with hypothesis Consistent with hypothesis Scientific Methods Observation Background Research Hypothesis/Predictions Question Experiment Not consistent with hypothesis Data analysis Answer? T Consistent with hypothesis Conclusion

What happens when you add N in the system? Background Soybean CO2+H2O +light C6H12O6+O2 N2 NH3 Photosynthesis Nitrogen Fixation Rhizobia

Fertilizer in agriculture 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).”

Scientific Questions: How do rhizobia affect plant growth? How does nitrogen fertilization affect plant-rhizobia interaction?

Hypotheses Question1: How do rhizobia affect plant growth? Question2: How does nitrogen fertilization affect plant-rhizobia interaction? Hypothesis1:Rhizobia increase plant performance Hypothesis 2: Fertilized plants have fewer nodules than non-fertilized plants. Hypothesis is an educated answer to the question posed. It is “a tentative answer to a well-framed question—an explanation on trial” (Campbell and Reece 2008).

Predictions Question1: How do rhizobia affect plant growth? Question2: How does nitrogen fertilization affect plant-rhizobia interaction? Hypothesis1:Rhizobia increase plant performance Hypothesis 2: Fertilized plants have fewer nodules than non-fertilized plants. Prediction 1: Rhizobia inoculated plants will have greater biomass than non-inoculated plants Predictions are “what we would expect to happen or what we would expect to observe if this idea were accurate” (Understanding Science 2014b). Prediction 2: fertilized plants will have fewer nodules than non-fertilized plants.

1) How do rhizobia affect plant growth? How can we test it? Experiment 1) How do rhizobia affect plant growth? How can we test it? + Control Treatment 1 + Treatment2 -Legume with no rhizobia --Legume wit rhizobia -Legume with Fertilizer (Note: This treatment is not necessary to address this specific questions but it tests whether rhizobia and fertilizer provide the same resource.) Controls are treatments against which manipulations are compared (Karban and Huntzinger 2006). Control group is “a group of individuals or cases matched to an experimental group and treated in the same way as that group, but which is not exposed to the experimental treatment or factor that the experimental group is” (Understanding Science 2014c). 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.

Experimental Design Control Replication Randomization

Experiment Replication + Repetition of a experiment to test the validity of its conclusion + + + As Replication is the establishment of independent multiple plots or observations within the same treatment or comparison group (Gotelli and Ellison 2004). Replication increases confidence in experimental results. +

Randomization + -Assign treatment randomly to an experimental group -Eliminate researchers’ bias or judgment Plots and observations should be randomly assigned to the treatment or control group (Gotelli and Ellison 2004) and this can be accomplished by students flipping a fair coin, rolling a fair dice or using a computer algorithm to generate random numbers

Plot a prediction graph on your worksheet ??? Plant Size Predictions in graph. Control Rhiz (+) Nitrogen (+) +

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

Plot prediction graphs on your worksheet Predictions: Predictions Plot prediction graphs on your worksheet Plant Size # Nodules N (-) N (+) N (-) N (+)

Experimental Design Combining Experiment 1&2 Question 1 n = 10 n = 10 n = 10 n = 10 Question 2 Each group: 4 treatments x 2 rep = 8 samples Class total = 40

After 1 month…. Record: Plant height (cm) Number of leaves Number of nodules Aboveground biomass Belowground biomass 3) Plot graphs using the class data -ruler -balance (sensitive one) -tray -bucket for soil -microcentrifuge tube -forceps -paper bag) -box to collect all the trays and pots -scissors -datasheet