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The acacia species is known as a stabiliser plant, meaning it is quick to regenerate or spawn in harsh environments such as low water and nutrients areas (Morcombe, 1970). These harsh environments are desirable for the species, with the acacia falcate thriving in full sunlight and a well drained position (Morcombe, 1970).
The aim of the experiment is to watch the growth and structural change of the Acacia falcate in four different environments. In this experiment I believe that the introduction of fertilisers and sorghum will have a detrimental effect on the growth and change in structure. Acacia falcate is a species which is well known for living in harsh environments where many other plants could not survive (Morcombe, 1970); when they are introduced to soils which are full of nutrients, and have to compete against another species, it will have an unfavourable effect on the growth and structure of the Acacia falcate. There are examples of Australian native plants that have suffered negative effects from an increase of nutrient concentrations in soils. For example "field and glasshouse experiments on the health and sclerophyll species have shown that added P can reduce the survival of seedlings" (Specht 1963, Heddle and Specht, Groves and Keraitis 1976)
This experiment shows the results of 1 one glasshouse experiment on native Acacia falcate in different environments. The four different environments are:
1) Acacia falcate
2) Acacia falcate with fertiliser
3) Acacia falcate with Sorghum (grass)
4) Acacia falcate with Sorghum and fertiliser
All four experiments were placed in 12 cm diameter pot plants which were13 cm in height. The seeds were planted in these pots on the 9th of February. Initially there was no fertiliser added to pots. The soil used in the pots consisted of native potting and sand in even quantities. In each environment, 8 seeds in total were added to the pots. So for experiment 1 and 2, 8 acacia falcate seeds were added and in experiment 3 and 4, 4 acacia seeds and 4 sorghum seeds were added.
The fertiliser used in experiment 2 and 4 is diluted NPK fertiliser (Aquasol). The fertiliser was made up of 0.3 grams in 125 ml of tap water. The glass house temperatures at day reached 26°C, and at night were18°C. The plants were watered once a day and the fertiliser was added to exp 2 and 4 once a week with 50ml of diluted fertiliser. The initial height was taken before the fertiliser had been added to any of the experiments. The average height of the plants was recorded each week and in the later weeks the amount of plants with and without phyllodes was counted as well. To ensure there was no bias in the results, the pot plants were numbered and observations were recorded blindly, without knowing which environment existed in each of the pot plants. The recorded heights, number of phyllodes and pH of the soil were analysed by using Microsoft excel to create both line and bar graphs.
Figure 1. shows the initial average plant height of the four different environments.
This graph shows that there is no dramatic change in the heights of the plants; this result is primarily based on the fact that these plants are early in development and that no fertiliser has been added to experiments 2 and 4. The standard deviation is also very similar, demonstrating that all the plants have been under the same conditions.
Figure 2. Shows the average height of each environment over the 8 week period.
This graph demonstrates that the experiment 2, which consists of acacia falcate and the fertiliser, has the highest average height, meaning that the increase of nutrients in the soil had a positive effect on the growth of the plant. It supports the idea that Acacia falcate is a species which can live in both high and low nutrient environments, and from the results of experiment 2 we can see that fertilisers will lead to an increase in the average height of the plant. The datum also showed that the environments which consisted of both the Acacia falcate and the grass seemed to have a lower average height. The standard deviation and average height in weeks 1 to 4 are very similar, showing that there are no significant changes in the early stages of development, but in the later stages the acacia with fertiliser increases in height and the standard deviation becomes larger and much more irregular. This could be the result of many things, such as the mechanism of the plant not using the nutrients or some dying in the later stages.
Figure 3. Shows the amount of plants with or without phyllodes in each environment.
The results show that the environments with fertiliser have a greater percentage of phyllodes when compared to those without fertiliser, this result indicates that the increase in the soil's nutrients due to adding fertiliser has allowed the acacia falcate to produce more phylloids.
Figure 4. pH levels found in the soil of each treatment
The results show that the pH levels are similar between the four different environments. The pH for all environments is around 6.3, meaning that adding the fertiliser and sorghum did not affect the pH level of the soil. Additionally, the standard deviations calculated are all relatively close; however both environments with fertiliser have a slightly greater standard deviation. This could be due to the fertiliser in the soil causing the pH to increase or decrease.
The introduction of fertiliser and sorghum into the acacia falcate resulted in major findings. Firstly, the introduction of sorghum decreased the average height found for environment 3 and 4. Secondly, the fertiliser had a positive effect on the average height of the acacia falcate and the percentage of acacia falcate with phllyodes.
My hypothesis at the start of the report stated that I believe the introduction of fertilisers and sorghum will play a detrimental role on the growth and change of structure of the acacia falcate. In regards to the introduction of sorghum, my predictions were supported by the results. Figure 2 demonstrates that the AF+S is has the lowest average height after 8 weeks, and that the AF+fert+S has a higher average height than AF only. In both of these environments the Acacia falcate has to compete with the sorghum for nutrients; this circumstance is unusual for the acacia species, as they are well known for living in harsh environments in which most other plants cannot survive (Cronin, 2008). One of the reasons the average height of the Acacia falcate may have decreased is because the sorghum is better adapted to high levels of nutrients, and it inhibits the acacia from reaching the same height as it does in the first environment.
In a report based on the study of grasses competing for nitrogen, it has been shown that some plants are better adapted to compete against other species when the nutrient levels are high or low. This study has revealed that that all native grasses were competitive at low nitrogen levels, but only one was competitive at high nitrogen levels (Badgery, Kemp, and King, 2005). This is reflected in the results of the experiment, as the acacia falcate showed that it was better able to compete against the sorghum in rich nutrient soil compared to low nutrient soil.
The introduction of fertiliser into the soil of environment 2 and 4 showed that the fertiliser had a positive influence on higher average height and percentage of phyllodes present. These results opposed my predictions of the fertiliser have detrimental effects on the growth and development of the plant. Even though the fertiliser may have increased the final average height and the percentage of phyllodes, there still could have been negative effects. The more fertiliser that was added to the acacia falcate the greater the standard deviation became. This could have been because of the fertiliser in the soil. The fertiliser had a tiny impact on the pH of the environments but all were very similar, but the fertiliser may have acted as a toxin and resulted in death.
In a report, when phosphate was added to the low nutrient soils of the Hawkesbury very much like the soils in environment 1 and 3. In the study t showed in the highest nutrient-addition treatments there was "almost a complete morality, including both seedlings and plants". This shows that even though the fertiliser had a positive effect on the growth and percentage of phyllodes, the adding of fertiliser to the normal environment of the acacia falcate could have serve effect on the species. by affecting seedlings and other biological mechanisms. (Morcombe, 1970) (Thomson and Leishman 2004).