Date of Award
Master of Science
Ecology and Evolutionary Biology
Edward E. C. Clebsch
John P. Witherspoon, Frank W. Woods
The purpose of this investigation was to study the mechanism that allows Sassafras albidum to maintain itself in relatively pure stands through many successional stages. Sassafras albidum is a common woody member of the old field community in Tennessee, invading in the early seral stages and surviving into the mature forest. Compounds known to be inhibitory to plant growth have been isolated from sassafras by other investigators. The presence of these terpenoid compounds in various organs of this plant suggests the existence of a possible allelopathic interference mechanism.
A survey of the internal and external herbaceous ground cover revealed the presence of then species which consistently occurred outside of the canopy. Seven species were also detected which existed predominantly beneath the sassafras canopy. It was suggested that annual herbs were being effectively excluded from the understory flora.
Various components of the sassafras environment were subjected to chemical analysis. Aqueous leachates of leaves and litter were extracted with steam distillation and intact samples were treated with acetone extraction. Qualitative and quantitative estimates of the phytotoxic compounds were accomplished by using two gas chromatographic systems each equipped with flame ionization detectors. The influence of these compounds on growth of germinating seeds was evaluated using the method described by Muller (1964).
The presence of several phytotoxic terpenes was demonstrated in canopy washings, litter, and in three size classes of roots and their possible ecological significance suggested. These compounds, including 2-pinene, a-phellandrene, euganol, safrole, citral, and d-camphor, were isolated within and outside of sassafras stands.
Germinating seeds treated with aqueous leachates of leaves, litter and canopy washing showed varying degrees of radicle reduction. Seeds germinated on soil discs obtained from beneath sassafras stands demonstrated statistically significant reductions for four of the test species; while seeds overwintered in sassafras litter displayed significant reductions for all species. A positive correlation between a-phellandrene concentration and reduction of radicle growth was noted for two species, Acer negundo and Ulmus americana.
Influx of seeds into three study areas was monitored for the summer of 1970; studies were also conducted in these areas to evaluate the buried viable seed populations. It was concluded that sufficient numbers of incoming and buried seeds were available to support a richer and more abundant understory flora than was evident from the floristic and vegetational survey.
This investigation provided important results which indicated that Sassafras albidum has many modes for releasing phytotoxins into the environment. Indications were also present which suggest that these modes operate at various times of the year to continually influence the surrounding environment.
Gant, Robert Edward, "The Allelopathic Influences of Sassafras albidum in Old Field Succession in Tennessee. " Master's Thesis, University of Tennessee, 1971.