Allelopathy in Trees Exploration
Pat Boleyn, Lane Community College
Location: Oregon
Abstract
Adapted from: An Aromatic Adventure with Allelopathy: Using Garlic To Study Allelopathy in the Classroom. By: Shimabukuro, Mary A., Haberman, Vickie, American Biology Teacher, 00027685, Apr2006, Vol. 68, Issue 4
Allelopathy is defined as any direct or indirect harmful or beneficial effect of one plant on another through production of compounds that escape into the environment. The most common usage of the term refers to the detrimental effect of one plant on another.
Allelopathic compounds can be released from plants in various ways including decomposition of plant residues, root exudation, leaching, and volatile emissions. Allelochemicals may assist plants by reducing competition from neighboring plants and providing protection from predators and pathogens. Often these chemicals inhibit seed germination and root growth of young neighboring plants with less effect on mature plants (Shimabukuro 2006).
Allelopathy is a complicated phenomenon. Reduced plant growth observed in many claims of allelopathy could be due to plant competition for water, mineral nutrients, carbon dioxide or root zone oxygen. Other factors could include pH changes or an altered osmotic potential of the soil as plant residues decompose. In addition, undecomposed plant material in soil may stunt plant growth due to immobilization of nitrogen.
For these reasons, much of our understanding of allelopathy comes from studies that rely on bioassays. A bioassay is defined as the determination of the relative potency of a substance by comparing its effect on a group of test organisms or cells using appropriate controls" (Shimabukuro, 2006).
However, allelopathy studies using bioassays are criticized because they do not approximate the conditions in natural ecosystems (Singh et al., 2001). Many of the problems described can be overcome by using a volatile allelopathic agent (airborne communication) such as garlic, or perhaps other volatiles that come from trees.
This class based undergraduate research project was used in a forest biology 102 course by Pat Boleyn, at Lane Community College in the biology department to examine allelopathy in trees.
Student Goals
- Conduct a scientific experiment
- Practice the scientific method, or approach
- Write a technical report
Research Goals
- Do volatiles from crushed tree needles inhibit seed germination of lettuce seeds & subsequent seedling growth?
- Does ph changes influence seed germination of lettuce seeds in the presences of crushed tree needles?
Context
This course based research project is used in a 10 week forest biology 102 course for a group of about 24 students. I give the students about 1 week to conduct this CURE. The students need to be introduced to critical thinking, scientific method and approach, the experimental design (introduction), report writing, and the concept of allelopathy.
Target Audience:Non-major
CURE Duration:A few class periods
CURE Design
Students are introduced to the scientific method through mini lectures and discussions, and given a template for experimental design and report writing. Students work in teams of 4, and can choose how they would like to crush their conifer trees to extract the chemicals. They also can choose additional tree species, to those that I assign, to observe their allelopathic effects. They develop hypotheses about which trees they think will have greater allelopathic effects on seed germination of lettuce seeds.
The stakeholders outside of the classroom are those that care about undergraduate research. So, your group is one. We have not developed a way to share the data collection effort of the class with the larger research community yet.
Core Competencies: Analyzing and interpreting data, Asking questions (for science) and defining problems (for engineering), Planning and carrying out investigations
Nature of Research:Basic Research
Tasks that Align Student and Research Goals
Student Goals ↓
The methods for the student's scientifc experiment are below:
Procedure Part 1 (Each team of 4)
1. Crush the plant material from all of the trees provided, with a grater or mortar and pestel.
2. Weigh 1.0 g samples of each crushed trees on a triple beam balance using the weigh boats.
3. Place the crushed tree materials in separate petri dishes, each containing 2 pieces of Whatman #1 filter paper, and 25 lettuce seeds. The sixth petri dish will contain only the lettuce seeds and the filter paper. This will be the control. Use the little scooper and white paper to count lettuce seeds on. They are small and hard to count.
4. Add 3 ml of water, record the ph and seal the dishes with masking tape, label on the bottom part of the dish with your team name, date, and contents of the dish, and place back on the cart in your tub to be incubated for three days under classroom conditions. Make sure you label the bottom of the dishes. Place masking tape on edges of petri dishes.
5. The petri dishes per table should contain the following: dish 1: Douglas-fir and lettuce seeds; dish 2: Ponderosa Pine and lettuce seeds; dish 3: Incense and lettuce seeds; dish 4 Western Juniper and lettuce seeds dish 5: Just lettuce seeds
Procedure Part 2
6. At the start of the next class, measure lettuce seedling length and ph of each dish. A length of zero may be recorded for seeds that do not germinate.
Students conduct team experiments in allelopathy using the steps of the scientific method.
Prepare a report as follows (team graphs and tables, but individual reports)
Report (to be completed during the next class with your team):
Create a table and graph of your results. Label this and give it a title. Explain what your results mean in at least a page. The table should include the length of lettuce seeds in each of the 7 petri dishes. You can also include labeled sketches of the petri dishes, or ones you produce using a computer program.
Also discuss what the strengths and weaknesses of this study
What you learned about allelopathy and plant volatiles
Folklore and cultural uses of one of the trees from your research
Why a control was necessary and what the control demonstrated
How you might apply this knowledge to landscaping or to your life
3 references in APA format
Instructional Materials
Please see the attached lab with all of the instructions. I also have a short lecture on the concepts of allelopathy. I have a syllabus that details the week for the experiment to take place. The grading is outlined in the syllabus and includes the lab grade itself, and a grade for their reports and class discussion. The materials list is in the attached lab.
Allelopathy in Trees Lab (Microsoft Word 2007 (.docx) 23kB Sep26 20)
Assessment
Technical report, poster, or slideshows, that are graded. Class discussions are also graded for participation.
Instructional Staffing
I am the instructor that helps them with all aspects of the work: Pat Boleyn
Author Experience
Pat Boleyn, Lane Community College
I have developed this CURE in a forest biology 102 class and it was successful. The students were extremely motivated to think critically and that is why it is a great project for them.
Advice for Implementation
This was a very successful class project. You will need a greenhouse or safe place with no blowing air, for the petri dishes to sit for several days. The seeds grow fairly quickly however (in about three days). The software needed could include a spreadsheet for their results, or just MS Word or google docs for making tables and writing their reports.
Iteration
The final class discussion is where the students get to review the class results and discuss the strengths and weaknesses of their experiments. They also have a strengths and weaknesses section in their final reports or posters.
Using CURE Data
There is no authorship for this project at this point. The students share their results among their classmates and with other science students, as part of an annual undergraduate fair, organized by the Lane Community College Science, Math, and Engineering Division. This is an educational exercise to practice critical thinking and learn the scientific method, and also to write scientific reports, posters, or slideshows.
Resources
An Aromatic Adventure with Allelopathy: Using Garlic To Study Allelopathy in the Classroom. By: Shimabukuro, Mary A., Haberman, Vickie, American Biology Teacher, 00027685, Apr2006, Vol. 68, Issue 4