a comparison of water potential and mechanical strength of
TRANSCRIPT
Pepperdine University Pepperdine University
Pepperdine Digital Commons Pepperdine Digital Commons
Featured Research Undergraduate Student Research
2012
A Comparison of Water Potential and Mechanical Strength of Tip A Comparison of Water Potential and Mechanical Strength of Tip
and Base Leaves in Heteromeles arbutifolia and Base Leaves in Heteromeles arbutifolia
Aaron Tsai Pepperdine University
James Maynard Pepperdine University
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Recommended Citation Recommended Citation Tsai, Aaron and Maynard, James, "A Comparison of Water Potential and Mechanical Strength of Tip and Base Leaves in Heteromeles arbutifolia" (2012). Pepperdine University, Featured Research. Paper 44. https://digitalcommons.pepperdine.edu/sturesearch/44
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A Comparison of Water Poten1al and Mechanical Strength of Tip and Base Leaves in Heteromeles arbu-folia
Abstract
Introduc1on
Materials and Methods
Results
Conclusion
Aaron Tsai and James Maynard, Pepperdine University, Malibu, California 90263
Literature Cited
Acknowledgements
Study Site Heteromeles arbu-folia, commonly known as, Hollywood, is a plant that is extremely common in the California Chaparral ecosystem. It was observed that with Hollywood, the leaves grow on the Ips of the branches predominantly. However, there are leaves that grow on the base of the branches that appear to be equally as healthy. The purpose of this invesIgaIon was to determine whether the leaves that grow at the Ips of the branches or at the base of the branches were beKer suited to benefit the rest of the plant. Our hypothesis was that the leaves at the Ips of the branches would be beKer suited to benefit the rest of the plant due to their beKer access to sunlight, as the rest of the plant does not overshadow them. We determined which leaves would be beKer suited to benefit the plant by measuring the water potenIal and mechanical strength of leaves at the Ip and bases of branches on Heteromeles arbu-folia plants across the street from the Pepperdine cross. Samples were collected from Heteromeles arbu-folia specimens that were both in the sun and in the shade. APer the results were compared, the plants in the sun showed that leaves at the base were mechanically stronger than those at the Ip, while plants in the shade showed leaves at the Ip were mechanically stronger. As for water potenIal, base leaves had higher water potenIal across the board.
To test our hypothesis, we chose a test site that was abundant in Heteromeles arbu-folia so we could test mulIple plants in mulIple locaIons. Across the street from the Pepperdine Cross proved to be a perfect locaIon. The first step in the process was to obtain samples. Two specimens of these species were first located. Two of these plants were in the shade, the other two were in the shade. One healthy leaf was then clipped from the Ip and base of each of the plants in both the shade and sun. Four of these leaves (one from Ip and base from each plant) were tested for water potenIal using a pressure chamber. The remaining samples were then tested for their mechanical strengths using the Instrom Mechanical TesIng Device. The results from these tests for all the leaves were then compared and conclusions were drawn.
• The leaves at the Ip of the branch of the shaded plant are mechanically stronger than the leaves at the base of branch.
• The leaves at the base of the branch of the non-‐shaded plant are mechanically stronger than the leaves at the Ip of branch.
• The leaves at the Ip and base of the branch of the non-‐shaded plant have the same water potenIal.
• The leaves at the base of the shaded plant have a higher water potenIal than the leaves at the Ip of branch.
• Shaded Heteromeles arbu-folia directs more of its nutrients and water to the Ips of the branches than the base of the branch.
We would like to thank Dr. Stephen Davis, Taylor Stucky, and Nick Huron for guiding us through this project.
Discussion This experiment was performed in order to see the difference between the leaves at the base and Ip on the branches of Heteromeles arbu-folia. It was hypothesized that the leaves at the Ip of the branches would benefit more than the leaves at the base of the branch because of its higher exposure to sunlight. Our data shows that the leaves at the Ip of the shaded H. arbu-folia are more hydrated and have mechanically stronger leaves compared to the leaves at the base of the branch. This is significant because it shows that the water and nutrients, which come from the base of the plant, are directed more to the leaves at the Ip than the leaves at the base of the branch. The plant in the shade wants to promote new growth at the Ip of the branch, while the plants in the sun direct its water and nutrients in order to survive its drier environment
Our study site was across the street behind the Theme Tower on the Pepperdine University campus.
Figure 1: James Maynard working hard with the Instrom Mechanical TesIng Device.
Figure 2: Aaron Tsai using Pressure Chamber to find water potenIal.
Figure 3: James Maynard collecIng samples of Heteromeles arbu-folia from our study site.
Figure 4: Heteromeles arbu-folia specimens at our study site.
Figure 5: Our group next to the Instrom Mechanical TesIng Device.
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Heteromeles arbu-folia is a plant that is extremely prevalent in the California Chaparral ecosystem. It lives in many locaIons and the different locaIons they live in have an influence on how successful the plant is in terms of survival. Our hypothesis is that leaves on H.arbuIfolia plants that are on the Ips of the branches will be stronger than those at the base. This is because they will have beKer access to sunlight and are not overshadowed by the rest of the plant. In order for a plant to funcIon properly, its leaves have to contribute to the plant by carrying out photosynthesis. If the leaves have higher mechanical strength and lower water potenIal, then they will be more likely to survive, and thus, benefit the plant in the future. Mechanical strength is important when talking about leaves because it shows how much stress and strain a leaf can take before it tears, thus causing damage to the plant. Stronger leaves mean they will be more suited to stand against the forces of nature and thus, be able to survive to benefit the plant. Water potenIal is significant because it shows how hydrated the leaves are. Leaves that have lower water potenIal have a higher level of hydraIon, which is necessary for the plants survival. Thus, plants with lower water potenIal will be more beneficial to the plant than leaves with a higher potenIal.
Balsamo, R. A., Bauer, A. M., Davis, S. D., & Rice, B. M. (2003). LEAF BIOMECHANICS, MORPHOLOGY, AND ANATOMY OF THE DECIDUOUS MESOPHYTE PRUNUS SERRULATA (ROSACEAE) AND THE EVERGREEN SCLEROPHYLLOUS SHRUB HETEROMELES ARBUTIFOLIA (ROSASEAE). American Journal Of Botany, 90(1), 72. Burk, J. H. (1978). Seasonal and Diurnal Water PotenIals in Selected Chaparral Shrubs. American Midland Naturalist, 99(1), 244. Wagner, K.R., Ewers F.W. and S.D. Davis. (1998). Tradeoffs between hydraulic efficiency and mechanical strength in the stems of four co-‐occurring species of chaparral shrubs. Oecologia 117: 53-‐62.