Grade Level: 6th to 10th; Type: Life Science: Botany
Determine if the allelopathic chemical produced by the Black Walnut tree biodegrades immediately or can persist in the soil over several days.
- What is Allelopathy and Juglone?
- What is the meaning of the term biodegradable?
- Does the allelopathic chemical produced by the Black Walnut tree biodegrade immediately once it enters the soil?
- Does the allelopathic chemical produced by the Black Walnut tree tend to persist in the soil over an extended period of time?
- How did the allelopathic chemical juglone react with the tomato plants?
- Tomato plant seeds
- Small flower pots (or plastic cups)
- Distilled water
- Black walnut (leaves, bark, or roots), which can be obtained at www.scienceinabag.com/AllelopathyPage.html
- Metric measuring cup
- Plastic tablespoon
- Potting soil
- Setup 10 small flower pots (or cups with holes made in the bottom for drainage), and fill with soil.
- Using a marking pen label each pot as follows:
- Soil + Control day 1 and Soil + juglone day 1
- Soil + Control day 2 and Soil + juglone day 2
- Soil + Control day 3 and Soil + juglone day 3
- Soil + Control day 4 and Soil + juglone day 4
- Soil + Control day 5 and Soil + juglone day 5
- Place 20 black walnut leaves, bark (or roots) in a large pot and fill the pot half full with distilled water.
- Bring the leaf-water mixture to a boil. Boil the leaves and water for about 10 minutes. After 10 minutes, use a large spoon to remove the leaves from the water.
- Continue to boil the now extracted juglone solution for 20 minutes.
- After 20 minutes, allow the liquid to cool completely.
- Once the liquid has cooled, pour equal amounts of the solution into the five juglone labeled flower pots.
- Pour the same amount of distilled water into each control soil pot.
- Do not add excessive amounts of juglone to the point where the soil becomes muddy!
- Using a plastic spoon stir the mixture.
- Add one or two tomato seeds to both the control and the juglone soil pots labeled “day one” place them in a sunny location.
- The next day place a tomato seed in the soil labeled juglone “day two” and its corresponding control.
- Repeat the same procedure with the remaining soil pots over the next three days.
- If the soils appear to be drying out moisturize with a small amount of distilled water.
- Record in which soil pot the tomato seed began to germinate if any, and compare it to the growth seen in the control.
- Enter the results of the observation in a data table.
- As an extension project on day six begin measuring the heights of the tomato plants that have begun to grow, if the juglone did not prevent their germination.
- The data in the table can be visually displayed by plotting a bar graph of allelopathic chemical soil biodegradable vs. time on graph paper or a computer equipped with Excel, by listing the height along the vertical axis verses the length of time the juglone was in the soil along the horizontal axis.
Terms/Concepts: biodegradable, allelopathy, juglone, allelopathic effect, walnut toxicity, Black Walnut Tree, Do allelopathic substances tend to biodegrade in soil over time?
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