Allelopathy Abstract

Monica Ly, Nitin Kumar, and Thuy Le

CU Boulder, Fall 2006


We tested the effects of allelopathy on the germination of plants.  Allelopathy is a technique in which a plant suppresses the growth of another plant located in close proximity by emitting chemical compounds.  Since plants that grow nearby allelopathic plants are exposed to the allelopathy, they will grow less than if the allelopathic plant did not release chemicals into the surrounding soil or air. We hypothesized that the amount in which plants are exposed to allelopathy determines the rate of their growth.

In order to test this hypothesis, we placed a total of 90 radish seeds in moist napkins inside Petri dishes within glass containers in three different environments.  In our control group, we placed 30 radish seeds in an environment that was not exposed to any form of Juniper allelopathy.  In our second group, we placed 10 grams of sprigs of Juniper around another 30 radish seeds.  In our third and final group, the last 30 radish seeds were germinated in a Juniper extract we made by mixing chopped up sprigs of Juniper and water. We predicted that the group with the most contact with allelopathy, the group growing in the Juniper extract, would germinate and grow the least out of all the groups.

Our results indicated that the germination rate of the control, the Juniper sprigs, and the Juniper extract were not significantly different. The outcome was 30 out of 30 for the control, 29 out of 30 for the Juniper sprigs, and 24 out of 30 for the Juniper extract. By running an Analysis of Variance (ANOVA) statistical test for germination, we found that the results were .978 and .491 for the control, .978 and .600 for the Juniper sprigs, and .491 and .600 for the Juniper extract. The length of the radish seed germination was significantly different. The average length of the control was 54.8mm, 48.8mm for the Juniper sprigs, and 33.2mm for the Juniper extract. The control was .598 and .025, the Juniper sprigs were .598 and .087, and the Juniper extract was .025 and .087.

Our results are consistent with predictions based on our hypothesis. One problem pertaining to our experimental method was that not all the containers had equal exposure to light. We only used two lamps for nine containers of plants because we did not want to overexpose the radish seeds to light. Another problem with our experimental method concerns our measurement of radish plant growth. By simply measuring the lengths of the small germinated radish seeds with a ruler, this may not have been the most accurate method. However, our conclusions are valid because these potential problems do not necessarily affect the germination and growth data in any significant way that would skew the results. We found that the radish seed control groups grew the longest; the radish seeds surrounded by the Juniper sprigs grew, and the radish seeds exposed to Juniper extract grew the least. Based on these results, the plants that are exposed to allelopathic chemicals through the air are not significantly changed. The plants that are in direct contact with allelopathy, like through the soil, are significantly affected in length. From our results, we have a new insight about the relationship between allelopathy of Juniper and the germination and growth of neighboring plants. Not only does the presence of Juniper affect the germination and growth of neighboring plants, but perhaps the distance between the Juniper and other plant may increase or decrease the effect of JuniperŐs allelopathy. This would be consistent with our results because the sample that exposed radish seeds directly with Juniper extract had the least growth and germination.