The results were collected in terms of how many seeds germinated per treatment (all 8 Petri dishes) depending on the concentration, as well as in terms of the root length. This meant that results were collected for seed extracts, bark extracts and leaf extracts, depending on the concentration (100%, 50%, 25%, 12.5% and 0%) making up a total of 15 experiments, each containing a total of 8 Petri dishes (80 seeds). The findings for the seed extracts indicated that at 100% concentration, a total of 73 Raphanus sativus seeds germinated, while at 50%, a total of 74 germinated. At 25% 74 germinated, at 12.5% 78 germinated, while at 0% 77 germinated. The mean root lengths were 6.8, 8.3, 6.6, 7.5 and 4.9 cm respectively, with standard deviations of 4.745, 4.17, 4.12, 3.52, and 2.89. These results are indicated in table 1
TABLE 1 Seed Germination Data
|Seed Extract Concentration||Number of Seeds Germinated||Mean Root Length||Standard Deviation|
The results for the bark treatment in terms of concentration were as indicated in table 2 using the same parameters as above:
|Bark Extract Concentration||Number of Seeds Germinated||Mean Root Length||Standard Deviation|
For the leaf treatment were as indicated in table 3 below:
|Leaf Extract Concentration||Number of Seeds Germinated||Mean Root Length||Standard Deviation|
|Analysis of Variance (One-Way)|
|Source of Variation||SS||df||MS||F||p-level||F crit|
The hypothesis being investigated was: “It is expected that the concentrations of Juglans nigra allelochemicals would have a negative relationship with Raphanus sativus (radish) germination and growth.” This, therefore, dictated that the results or findings had to display a statistically significant negative correlation between the concentrations of the extracts and the mean germination of the seeds in all the experiments carried out. Of particular importance was, therefore, the mean seed germination for each concentration, the mean root length for each concentration and the concentration of the extracts. This therefore means that the graph comparing the mean root germination for each treatment, as well as the one comparing the mean seed germination for each treatment were quite important, as they gave an overview picture of the experiment, both in terms of comparing the findings across the concentrations, as well as across the three treatments. This helped in establishing the degree of allelopathy at the different concentrations, as well as the different levels of allelochemicals in each of the three treatments (bark, seed and leaf extracts) two key goals of the experiment.
The findings for the seed extract indicated a seemingly upward trend in the number of seeds germinated and a seemingly downward trend in the mean root lengths of the germinated seeds. While the first finding is in line with the expected hypothesis, the second finding concerning the mean root lengths does not conform to the hypothesis, as the expected outcome would be that the root lengths would gradually increase in length as the concentration was reduced, hence translating to a gradual increase in the mean root lengths with de crease in concentration. As such, the mean root length should have been highest at a concentration of 0% and the lowest at a concentration of 100%. Furthermore, the number of germinated seeds does not provide sufficient support for the hypothesis, as the difference in the number of germinated seeds between the highest concentration at 100% and the lowest concentration of 0% is just 4 seeds. Finally, the positive gradient in the graph of mean root length against concentration goes contrary to expectation. It indicates that the mean root length increases with increase in concentration, hence provides a perfect picture of how much the findings do not conform with the hypothesis, more so if compared to the line indicating the findings of the leaf extract experiments. The bark extract findings also display non-conformity to an extent, though not as pronounced as the seed extract findings. The bark extract findings when it comes to mean root length, do not conform with the expected findings, as the highest mean is 8.5 at a concentration of 50%, while the lowest mean is actually 4.4, achieved ironically at a concentration of 0%. The findings for the two treatments (bark and seed) actually serve to undermine the hypothesis, as the mean root lengths, in particular, seem to suggest the absence of allelopathy altogether. This is due to the fact that the expected pattern indicating a negative correlation between concentration and germination, as well as root length does not emerge, suggesting either the absence of allelopathy, or the absence of allelochemicals within the selected extracts (the seeds and the bark).
The findings of the leaf treatment conform to the hypothesis, as the concentration of the allelochemicals did have a negative impact on the mean root lengths as well as the number of germinated seeds. In fact, a very clear pattern emerges in that the lower the concentration, the higher the number of germinated seeds; at 100% concentration, the number of germinated seeds was only 60 (75%) while at 0% the number of germinated seeds was 77 (96.25%), a clear indication of the existence of negative allelopathy. This is further confirmed by the findings on the mean root lengths which seem to increase with a decrease in extract concentration. Overall, the findings of the leaf extract do demonstrate the existence of allelochemicals, as out of the 5 concentrations, the control (0%) produced the best findings in terms of seed germination.
All in all, although claims by Jose (2002) regarding the existence of allelochemicals in Juglans Nigra have been proven accurate, the concentration in the various parts of the tree requires further exploration. This is because the experiment findings suggest either the complete absence of juglone in the bark and seed extracts or their existence in very low concentration. The findings also raise an interesting possibility, that perhaps the concentration of the juglone in the soil surrounding most Juglans Nigra trees is usually as a result of fallen leaves, although the fact that root extracts were not part of the experiment, makes arriving at such a conclusion a bit more difficult.
Jose, S. Black Walnut Allelopathy: Current State Of The Science. Chemical Ecology Of Plants: Allelopathy In Aquatic And Terrestrial Ecosystems. Springer, 2002. Print.
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