Ecological Interactions

Experiment 1: Effects of pH on Radish Seed Germination

Natural soil pH depends on the parent rock material from which it was formed and processes like climate. Soil pH is a measure of the acidity or alkalinity of the soil. Acidic soils are considered to have a 5.0 or lower pH value whereas 10.0 or above is considered a strong basic or alkaline soil. The pH of soil affects the solubility of nutrients in soil water and thus it affects the amount of nutrients available for plant uptake. Different nutrients are available under differing pH conditions.

In this experiment we will look at the effect of pH on the germination and growth rate of radish seeds in order to determine the range of pH tolerance for the seed. Acidic or basic water will be used in order to stimulate acidity or alkalinity in soil.

Materials

2 mL 4.5% Acetic Acid (Vinegar), C2H4O2

Permanent Marker

(3) 5 cm Petri Dishes

3 pH Test Strips

Radish Seed Packet

Ruler

2 mL 15% Saturated Sodium Bicarbonate (Baking

Soda) Solution, NaHCO3

*Paper Towel Sheets (cut to fit into the petri dish)

*Scissors

*Sunny Location

*Water

*You Must Provide

Procedure

1. Use the permanent marker to label the top of each of the three petri dishes as Acetic Acid, Sodium Bicarbonate, or Water.

2. Carefully cut three small circles from the paper towel sheets. The circles should comfortably fit within the bottom of the petri dish.

3. Place the circles in the dishes, and wet them with approximately 2 mL of each respective solution (acetic acid, sodium bicarbonate, or water).

4. Gently press the reaction pad of three, pH test strips onto the wet paper towels. Record your data in the first row of Table 1.

5. Arrange 10 radish seeds on each paper towel in each petri dish. Make sure the seeds have space and are not touching. Then, place the top of the petri dish on the bottom.

6. Place the petri dishes in a sunny or well-lit, warm place. Be sure to keep the paper towels moist for the length of the experiment with the appropriate solution if any of the towels dry out.

7. Observe the seeds daily for seven days, and record the number of seeds that germinate in Table 1. Note when the seeds crack and roots or shoots emerge). On the seventh day, record the lengths of radish seed sprouts (mm or cm).