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Which Part of the Walnut Tree Contains the Greatest Concentration of Allelopathic Substances?

based on 9 ratings
Author: Michael Calhoun

Grade Level: 6th to 9th; Type: Life Science: Botany

Objective:

This science project is to discover which tree tissue contains the most concentrated amount of Juglone.

Research Question:

  • What is allelopathy and Juglone?
  • Which juglone solution stressed the tomato plant first?
  • How did the juglone solution react with the tomato plant?
  • Which Black Walnut Tree part contains the most concentrated amount of juglone?

Allelopathy is a process by which a plant releases chemicals that can either inhibit or benefit other plants. Juglone is the allelopathic substance produced by the Black Walnut tree that works like an herbicide to prevent the germination and growth of plants near the tree.

Materials:

  • Six young tomato plants in pots
  • Black Walnut (hulls, leaves, bark, root, and stem tissue), which can be obtained at www.scienceinabag.com/AllelopathyPage.html
  • Metric measuring cup
  • Plastic storage containers
  • Large cooking pot
  • Permanent marker pen

Experimental Procedure:

  1. Gather six young tomato plants and place each in separate flower pots or cups.
  2. Using a marking pen label each flower pot or cup as follows: “hulls,” “leaves,” “bark,” “root,” “stem,” and “control.”
  3. Place 20 black walnut leaves in a pot and fill the pot half full with water.
  4. Bring the leaf-water mixture to a boil. Boil the leaves and water for about 10 minutes.
  5. After 10 minutes, use a large spoon to remove the leaves from the water.
  6. Continue to boil the now extracted juglone solution for 20 minutes.
  7. After 20 minutes, allow the liquid to cool completely. Once the liquid has cooled, transfer it to one of the plastic storage containers and label “leaves juglone solution.”
  8. Clean the pot thoroughly with soap and water.
  9. Place chucks of bark in a pot and fill the pot half full with water.
  10. Bring the bark-water mixture to a boil. Boil the bark and water for about 10 minutes.
  11. After 10 minutes, use a large spoon to remove the bark from the water.
  12. Continue to boil the now extracted juglone solution for 20 minutes.
  13. After 20 minutes, allow the liquid to cool completely. Once the liquid has cooled, transfer it to one of the plastic storage containers and label “Bark juglone solution.”
  14. Repeat the same procedure for the hulls, root and stem.
  15. Using a metric measuring cup measure 60 ml (about 2 oz) of leaf juglone solution and add this amount to the tomato plant labeled “Leaves.”
  16. Repeat the same procedure for the hulls, root, bark and stem.
  17. To the control just add 60 ml of water.
  18. Place all of the plants in an area where they will receive equal amounts of sunlight.
  19. Observe the plants each day for signs of stress (withering, stunting of growth, wilting, etc).
  20. If the soils appear to be drying out over the course of the investigation add additional water to the plants so that they stay moist.
  21. When the first tomato plant shows signs of stress end the investigation!
  22. Record the data in the table.

Terms/Concepts: Allelopathy, juglone, allelopathic effect, walnut toxicity, Black Walnut Tree, juglone toxicity, Which Black Walnut Tree tissue (hulls, leaves, bark, root, and stem) contains the most concentrated amounts of allelopathic substance?

References: Principles and Practices in Plant Ecology: Allelochemical Interactions, by K. M. M. Dakshini and Chester L Foy (CRC Press, 1999).

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