An experiment was conducted to determine the effect of the allelopathic compounds of Encelia Farinosa (brittle bush) on desert native annuals and non-native seed germination. The experiment was set up by putting native wild flower seeds in six Petri dishes and lettuce seeds in six different dishes. To three of each dish containing the different seeds, water was added as a control. To the three other dishes, a prepared brittle bush tea (filtered ground brittle bush leaves and water) was added. After a week’s time, the number of germinated seeds in each dish was counted.
The results showed that the allelopathic compound in brittle bush did have a significant effect on both the lettuce seeds and the native wildflowers when compared to their respective controls. However, the results showed no significant difference between the two means of the native seeds with brittle bush tea and the lettuce with brittle bush tea. This led to the rejection of our hypothesis and acceptance of the null hypothesis which stated that no significant difference existed between the two means. Introduction In the natural world, plants are in constant strain of exploitation and competition.
Through the evolutionary process, plants have developed many ways to help cope with various environmental stresses. Some plants overcome environmental strain by growing taller or deeper to extract as many resources as possible. Others resort to numbers and try to overwhelm their predators and competitors by population size. However, possibly the most interesting method many plants take is the use of chemicals to kill or inhibit predatory herbivores and competing plants. Plants that resort to this method of defense are known as allelopathic and the chemicals used by these plants are called secondary metabolites.
Nowhere is the struggle for resources more vital than in the desert. The use of secondary metabolites in desert plants is believed to be one of the most common defense mechanisms in the desert community. Among these allelopathic desert plants is Encelia Farinosa or more commonly known as brittle bush (Tesky 1993). The effects of the secondary metabolites used by brittle bush have been studied by ecologists for many years.
Due to limited exposure, many believe the effectiveness of desert allelopathic compounds on on-native species would be great because the evolutionary process would not favor the development of a defense against the secondary metabolites (Fritzke 2003). However, other research has shown brittle bush to be highly detrimental and effective against various desert annuals (wild flowers). It is believed that desert annuals are under double the stress due to the fact that they only survive for a very short season, not allowing evolution to favor the development of defense against the toxicity of brittle bush, and also are in fierce battle with the specialization of the brittle bush’s secondary metabolites (Kunze et al. 994).
In this experiment, a team of researchers set out to find the effectiveness of brittle bush in the detriment of seed germination of native desert annuals (wild flowers) and non-native species. It is believed that native annual seeds treated with the secondary metabolites from brittle bush will show a greater difference in seed germination than non-native seeds also treated with the secondary metabolites. We predict that the native seeds will germinate significantly less than the non-native seeds. Materials and Methods
To start the experiment, our team obtained several brittle bush leaves (about 30 grams worth). The leaves were then ground in a mortar for a period of two minutes. Fifteen grams of the ground leaves were weighed out then transferred into a large glass container. Once in the containers, 150ml of water was added to each of the containers. Then the water/leaf cocktail was allowed to sit for a period of twenty-four hours. After the day of soaking, the mixture was filtered through a paper towel into a different glass container, as to remove all the crushed leaves, leaving only the liquid.
Once the leaf extract mixture was complete, twelve Petri dishes were obtained. A piece of six-inch filter paper was placed at the bottom of each dish. Each dish was then labeled as follows; dishes one through three were labeled “water control lettuce”, dishes four through six were labeled “brittle bush lettuce”, dishes seven through nine were labeled “water control desert flowers”, and dishes ten through twelve were labeled “brittle bush desert flowers”. Then, twenty-five lettuce seeds were placed in dishes one through six and twenty five desert wildflower seeds were placed in seven through twelve.
In the dishes labeled “water control lettuce” and “water control desert flowers”, a measuring cup was used to add 12 ml of plain water to the seeds. In the dishes labeled “brittle bush lettuce” and “brittle bush desert flowers”, 12ml of the liquid solution obtained from the brittle bush tea was added. The twelve dishes were then covered and allowed to sit for a week. The desert wild flower consisted of flowers native to the Arizona desert that appear on an annual base.
An important note is that the two different types of seeds were exposed to the sun according to what was considered ample amount of time. For instance, the lettuce seeds called for partial sun. Therefore the seeds were exposed to the sun for part of the day, then shade for the rest. The desert wild flowers called for complete sun. They were left out in the sun at all times. After a one week time period, the dishes were opened and the number of germinated seeds within each of the dishes were counted and documented.