The Rhododendron genus can be found in many different habitats around the world but scarce in desserts, and dry forests as well as tundra regions. . Rhododendrons are studied from the xylem to the leaves, but we believe the secret is in the roots. Kong et al., found two different dimensions of root trait diameter across 96 subtropical woody species: a diameter related dimension that may integrate root construction, and possibly maintenance and persistence, with a branching density dimension that may express difference in root plastic responses to environment. We would like to address the question of what really goes on in the roots and if the anatomy and morphology of the roots are connected to the temperature tolerance of different rhododendron species. We also believe that Rhododendron with similar cold tolerances have similar fungi on their roots. The study site was the Helen S. Layer Rhododendron garden at Holden Arboretum. We studied the morphology, anatomy of six species of Rhododendron from three sections: Ponticum section (Maximum, Degronianum), Pentanthera section (Austrinum, Molle), and Tsutsuti (Yedoense, Indicum).
Effect of Environmental Changes on Phenological Variation of Leaf Functional Traits in Miconia and Piper Species04/05/2018
Several studies have proposed that a group of morpho-functional traits are key factors in determining the ecological strategy of plant species. Among these, five leaf morpho-functional traits are considered to be relevant in determining a plant's ecological strategy: leaf length, width, thickness, area, and specific leaf area (SLA). Here, I studied the variation in leaf functional traits within and between species of two genera of understory shrubs commonly found in the tropical rain forests of Costa Rica. In addition, I examined how these traits varied in two different light environments: forest-covered and full-light. I hypothesized that light availability has a direct impact on leaf functional traits and that the response of each genus is independent of the other. Leaves from Miconia and Piper species were collected in both forest-covered and full-light environments along two trails located in Alberto Manuel Brenes Biological Reserve, Costa Rica. Leaf length (F1,163=5.51, p=0.0201), leaf weight (F1,163=4.82, p=0.0296), and leaf area (F1,163=6.24, p=0.0135) varied significantly between genera and environment. Leaf length (F1,163=4.42, p=0.0370) and surface leaf weight (F1,163=4.59, p= 0.0336) varied significantly between forest-covered and full-light environments for both genera. Overall, the results show that leaf functional traits can vary as a result of phenotypic plasticity to varying amounts of light. Variance in other abiotic conditions, such as soil type and water availability may also have similar effects on phenological variation between different functional traits in plant communities of different environments.
Key Words: Functional trait, Piper, Miconia, Costa Rica, plasticity, light availability, abiotic
The problem: Eastern red cedar Juniperus virginiana is a native-invasive tree that is rapidly spreading across the Midwestern United States and has encroached as far as South Dakota and Nebraska. It is a serious problem in rangelands because cattle and sheep do not eat woody plants. We investigated the role of allelopathy, the chemical inhibition of one plant by another through the release of chemical suppressants or growth inhibitors into the soil. We wished to establish whether these plants were able to suppress the germination and growth of a dominant grass, big bluestem Andropogon gerardii.
Methods: We applied root exudate of J. virginiana to seeds of A. gerardii in petri dishes and applied distilled water as a control. We also compared germination and growth rates of A. gerardii in the presence and absence of oaks as potential competitors with the eastern red cedar trees.
Results: There was significantly lower germination of A. gerardii grown in the root exudate than controls of this species (grown in distilled water). This result demonstrated that J. virginiana contained significant allelopathic chemicals. However, we found no significant difference in A. gerardii germination between oak vs. no oak for the root exudate. In a subsequent experiment, we found no significant difference in relative growth rates between those growing with and without oaks and controls. Thus, the main allelopathic effect of eastern red cedar is in suppressing germination of this grass species. Allelopathy may be an important reason for the successful dispersal of this native-invasive species.