HandsOn 20 - Building a Rhizotron and Germinating Seeds
A rhizotron is a clear-walled chamber through which one can observe roots as they grow. Here we describe two alternative methods for studying root growth with simple rhizotrons. Method 1 involves the use of the rhizotron with a stagnant solution such as water or nutrient mixture. Method 2 involves the use of the rhizotron in a tub of solution with a fish tank aerator providing oxygen to the solution. Several variations in the concentration of nutrient solution are possible in performing the root growth experiment.
In addition to the materials needed to build the rhizotron itself, you will need the following materials:
The seeds must be germinated before they are placed in the rhizotron. Germination allows the seeds to grow a large enough root system so that they can be supported by the top edges of the rhizotron. Otherwise, the seeds are too small to place on the rhizotron.
2. Place some of the wet sheets of paper towel in the bottom of a petri dish, and place the seeds on top of this.
3. Cover the seeds with more wet paper towel, and put the cover of the petri dish on. Store in a warm, dark place. (Placing the petri dish in a black garbage bag to insulate it from heat and keep it out of the light works.)
4. On a daily basis, moisten the seeds and paper with water.
5. The seeds should be allowed to germinate until they are large enough to sit at the top of the rhizotron frame, supported by the plastic sides. The average germination times for commonly used seeds are: Peas-3 days, Barley-4 days, Beans-4 days, and Tomatoes-5 days.
2. Fill the rhizotron with the nutrient solution so that the solution reaches the top edges of the rhizotron.
3. After the seeds have been sufficiently germinated, select the largest seeds. Carefully place the selected seeds on the top of the rhizotron, and tuck the roots between the plastic pieces. More than one germinated seed can be placed in a rhizotron.
4. (Optional) Wrap a strip of black plastic garbage bag around the rhizotron. Make sure that the top edges of the plastic do not extend past the top edge of the rhizotron.
For root growth with oxygen, you will be placing the rhizotron in a tub of water so that the solution may be aerated. This requires that you have sufficient passage of solution from the inside of the rhizotron to the outside.
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