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How Much Does Acid Rain Hinder the Growth Height of Brassica rapa Plants Without Other Environmental Stressors? Author(s) Redacted Abstract: Brassica rapa plants are one of many plants in the environment that are affected by “acid rain”. According to the Environmental Protection Agency, acid rain is “a mixture of wet and deposited material from the atmosphere that contains a high acidity level of nitric and sulfuric acid.” The acidity of the mixture can stunt the growth of plants due to the lack of nutrients and the effect of the mixture on the tissue and roots of the plant. However, there are several other factors that need to be considered when observing the effects of acid rain on the environment. Such stressors that contribute include air pollutants, insects, disease, drought, or very cold weather. We tested the effect that “acid rain” had on the growth height of Brassica rapa plants by eliminating such stressors, in order to find the effect of only “acid rain” on the plant. The growth of the Brassica rapa plants was measured by comparing the height of watered plants to the height of plants exposed to “acid rain”. The relationship between the growths of the controlled was compared to the plants affected by “acid rain”. The height of the plants that were exposed to the “acid rain” measured much shorter than those of the controlled. The results showed a relationship between the difference in height, color, and mass of the Brassica rapa plants of both the independent and controlled plants. Introduction: Over the years, scientists, foresters, and others have noted a slowed growth of some forests. Leaves and needles turn brown and fall off when they should be green and healthy. In extreme cases, individual trees or entire areas of the forest simply die off without an obvious reason. After much analysis, researchers now know that acid rain causes slower growth, injury, or death of forests. Acid rain has been implicated in forest and soil degradation in many areas of the eastern U.S., particularly high elevation forests of the Appalachian Mountains from Maine to Georgia that include areas such as the Shenandoah and Great Smoky Mountain National Parks. Of course, acid rain is not the only cause of such conditions. Other factors contribute to the overall stress of these areas, including air pollutants, insects, disease, drought, or very cold weather. In most cases, in fact, the impacts of acid rain on trees are due to the combined effects of acid rain and these other environmental stressors. After many years of collecting information on the chemistry and biology of forests, researchers are beginning to understand how acid rain works on the forest soil, trees, and other plants. Methods: The plant Brassica rapa was grown in both a controlled environment and an environment that was manipulated by simulated acid rain (water and vinegar set to a pH balance of 4.) A station was set up that contained Styrofoam cells where the seeds would be planted, seeds, fertilizer, soil, anti-algal squares, cell wicks to assist water absorption, felt, and a water basin. Additional materials included spray bottles, a plastic cover from a shoebox sized container, saran wrap, skewers, and bees. Each trial, the control and experiment, consisted of 16 cells. The seeds were planted and cared for in the exact same fashion and manner aside from replacing the water being sprayed on the control with “acid rain” in the experiment. Both were sprayed with three puffs three times a week. To make the apparatuses that the plants would grow and live, wicks were placed in each cell and extended through the cell as to absorb water from the bottom into the cells. Then the cells were filled with soil, 2-3 fertilizer pellets, and 3 seeds, and then covered by saran wrap to prevent the soil from receiving the spray. Watering basins were created by filling shoebox sized plastic containers with water, adding the anti-algal squares to the water, putting one end of the felt into the water, putting the lid onto the container, and placing the remaining felt on the lid of the container. After the apparatus was assembled, the plants were watered with the contents of their respective spray bottle, using the plastic lid to prevent the control and experiment from being cross contaminated and from then on watered every 2 days in the same manner. They grew under fluorescent lights to simulate daylight, and the experiment lasted 40 days due to the short life of Brassica rapa. As the plants grew, skewers were placed alongside the plant so that they would grow upright. Within approximately two weeks, when flowering began to occur, bees were skewered and used for pollination. At the end of the experiment the plants were harvested and the number of leaves, number of pods, number of seeds, the weight, and the length were recorded for each surviving plant. Results: Control Plants 55 50 45 40 35 Height of plant (cm) 30 # of pods # of seeds 25 pre‐weight (g) 20 dry weight (g) # of leaves 15 10 5 0 1 2 3 Figure 1 Control Plants 4 5 6 7 8 Plant # 9 10 11 12 13 14 Experiment Plants 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Height of plant (cm) # of pods # of seeds pre‐weight (g) dry weight (g) # of leaves 1 2 3 4 5 6 7 8 9 10 11 12 13 Plant # Figure 2 Experiment Plants Figure 1 shows the results of the control plants. These plants were sprayed with “acid rain”. Figure 2 shows the results of the experimental plants. In the control group, 14 plants grew. In the experiment group, 13 plants grew. The average height of the control group is 24.3 cm while the average height of the experiment group is 8.8 cm. We also counted the number of pods and seeds per plant to see what affect the different liquids had on them. In the control group, the average number of pods was 9 with an average of 17 seeds, while the experiment had an average of 0.5 pods and 0.1 seeds. Most of the flowers of the experiment group never grew or died quickly after being sprayed with the “acid rain” solution. The leaves, however, did grow. The average number of leaves for the experiment group was 3. The control group had lots of flowers and leaves. The average amount of leaves for the control group was 4. We also noticed that within seconds of being sprayed with the “acid rain”, the green leaves became spotted white. The solution had an immediate effect on the leaves. Table 1 Control Data Plant # Height (cm) root length (cm) leaves pods seeds pre‐weight (g) dry weight (g) 1 7.5 4.2 5 0 0 0.01 0.01 2 7 2.2 5 1 0 0.04 0.04 3 15.5 3.7 5 3 7 0.26 0.04 4 16.7 4.8 3 2 3 0.27 0.03 5 30.5 4.4 4 18 5 0.47 0.1 6 31 2.6 3 26 3 0.59 0.14 7 34.6 3.9 3 17 52 2.02 0.38 8 36.3 4 0 11 30 1.25 0.25 9 39.4 6.5 5 12 33 1.5 0.31 10 30.2 4.1 4 5 32 1.14 0.24 11 27.5 4.1 2 7 37 1.15 0.22 12 16.6 3.2 9 4 9 0.28 0.08 13 31.4 4.3 3 20 24 1.06 0.2 14 15.8 4.4 9 3 6 1 0.2 Table 2 Experiment Data Plant # Height (cm) root length (cm) leaves pods seeds pre‐weight (g) dry weight (g) 1 19 5.9 11 0 0 0.28 0.04 2 16 2.6 6 1 1 0.37 0.06 3 13.5 1.4 0 4 0 0.01 0.01 4 8.3 1.7 5 0 0 0.03 <0.01 5 10.4 3 5 0 0 0.01 0.02 6 10.2 4.5 1 0 0 0.01 0.01 7 5.5 0.3 0 0 0 0.02 <0.01 8 2.3 2.5 4 0 0 0.02 <0.01 9 4.2 0.6 4 0 0 0.01 <0.01 10 9.2 5.4 0 0 0 0.02 0.01 11 6.4 3.7 2 0 0 0.01 0.01 12 4 1.6 4 0 0 0.01 <0.01 13 5.7 3.6 2 0 0 0.01 <0.01 Calculations/Error Analysis: Average number of leaves per plant Control: 4 Experiment: 3 Average length of plant including root (cm) Control: 24.3 Experiment: 9.1 Average length of root (cm) Control: 4.0 Experiment: 2.8 T-Test for entire plant length: Control: standard deviation (σ) = 10.76, n= 14, Z=8.45 Experiment: standard deviation (σ) = 4.96, n= 13, Z= 6.41 Discussion: The results of this experiment clearly show that the growth in plants subjected to “acid rain” is significantly hindered compared to those plants that received only water. The final length of the control plants was 15.2 cm longer on average than the final length of the experimental plants. By controlling the amount of moisture that comes from the soil, we were able to test whether it was the “acid rain” coming down on the part of the plant above ground that had any effect. There were some margins of error in this experiment. Although we did use saran wrap to try to protect the soil, this method was not completely accurate. Small rips in the saran wrap were hard to prevent and hard to fix, and they also meant that some water could seep through. To improve this aspect in a future experiment, it is suggested that a more durable material be used to prevent ripping and unwanted seepage. There were two pieces of data in particular that stood out. The average number of leaves per plant in the control group was very similar to the average number of leaves per plant in the experimental group. The average root lengths of the control and experiment groups were also very similar. This could indicate a correlation between root length and the number of leaves a plant grows. It is interesting that although the entire plant lengths of the experiment group were much smaller than the plant lengths of the control group, the root lengths were so similar. This tells us that perhaps we were able to prevent most of the “acid rain” solution from running into the soil, and therefore the roots of the experiment plants were able to grow as well as the control plant roots. References "Acid Rain Students Site: PH Scale." US Environmental Protection Agency. http://www.epa.gov/acidrain/education/site_students/phscale.html (accessed September 22, 2011). "Effects of Acid Rain - Forests | Acid Rain | US EPA." US Environmental Protection Agency. http://www.epa.gov/acidrain/effects/forests.html (accessed September 22, 2011). "What is Acid Rain? | Acid Rain | US EPA." US Environmental Protection Agency. http://www.epa.gov/acidrain/what/ (accessed September 22, 2011). Wisconsin Fast Plants Growing Instructions. North Carolina: Carolina Biological Supply Company, 2001. Print.