The Effects of pH on the Growth of
Snow Peas, Pisum sativum
Ryanne Karnes
Biology 402
April 19, 2008
Table of Contents
Introduction
- Pollution3
- Acid rain3
- Agriculture3
- Simulated Acid Rain and Cabbage Seeds4
- Effect of pH on Marine Phytoplankton5
- Water Hyacinths as Pollution Reducers6
- Simulated Acid Fog and Green Peppers 7
- Simulated Acid Rain on Epicuticular Wax8
- Topic Hypothesis10
Research
- Data Collection10
- Results13
- Figure 114
- Figure 214
- Statistical Analysis15
- Discussion15
- Acknowledgements18
Literature Cited 19
Abstract
This study was done to determine the effects of pH on the common snow pea, Pisum sativum. The effects of pH on peas can give an insight into what acid rain could do to crops across the nation if the amount of pollution continues to rise. The peas were divided into nine groups. Seven groups were watered with solutions of altered pH levels and two groups were watered with the controls, deionized and tap water. The plants watered with pH levels below 7 had the most growth in their height, while the plants watered with pH levels above 7 had poor height growth. A pH of exactly 7.0 produced similar results to the deionized and tap waters, which had vertical growth in between the low and high pH levels. There was no statistical difference among the vertical growth of the plants. However, the however had differences. The peas watered with tap water had more diameter growth than those watered with a pH of 11.0. There also was more growth in the peas that were watered with deionized water when compared to those watered with pH levels of 11.0 and 8.0.
Introduction
Air pollution has become problem in the last few decades and it is caused by a number of different factors including air conditioners, aerosols, the burning of fossil fuels and even natural environmental changes such as volcanic activites. The amount of air pollution is a problem because many of these pollutants can cause health problems such as asthma, lung disease, cancer, eye irritations and even death (Gifford, 2006). Two common air pollutants can lead to another kind of pollution that many people put into a category of its own, acid rain.
When sulfur dioxide and nitrogen oxide are released into the atmosphere, these molecules mix with the moisture in the air to form nitric acid and sulfuric acid and return to earth in the form of acid rain, fog, snow or dust. This is called acid deposition and it is more common in the eastern United States than it is in the western states (Washington Environment 2010, 1989). It is more common in the eastern states because the weather patterns carry pollution from the west to the east. It is also because of the numerous industrial factories adding to the pollution on that side of the country. There is no way to control where and when acid rain will fall since once it forms in the air, it becomes part of the weather pattern. When acid precipitation falls it can affect forests, fields, gardens, and aquatic plants. It also affects paint on buildings, erodes limestone structures and sculptures, kills or dwarfs trees, and reduces food crop yields (Kidd and Kidd, 2006).
In order to live a life where fear for the environment does not rule the decisions we make, it is important to know the effects that acid rain can have on human life. Although the direct impact on humans is limited, acid rain canaffectagriculture in Washington, the United States and worldwide. In 2002, the agricultural census showed the amount of land devoted to farming in the United States was at 15.3 million acres with about half being used for crop growth. The census also showed that in Washington alone agriculture was a 5.3 billion dollar industry (WSDA, 2004).As the atmospheric pollutions increase on the west coast, the weather patterns change and the possibility for acid rain rises, it becomes apparent that it could affect the state of Washington’s economy. Acid rain can cause damage to plants by eating away at the outer protective layer of the leaves,but the most damage is seen when the soil that the plants are grownin stays acidic instead of returning to neutral (Petheram, 2002).
Caporn and Hutchinson (1987) studied the effects of temperature, water, and nutrient conditions on cabbage seedlings. Their main focus was how these three conditions affected the seedlings when they were exposed to a single treatment of simulated acid rain. The acid rain used had a pH of 3.0. They put the seedlings in different environments and exposed them to a spray of acid rain in a greenhouse environment and an outdoor environment. After being sprayed with the simulated acid rain, the plants outside were protected from natural rainfall by being placed under glass sheets. This was done so the pH of the artificial acid rain spray was not altered by the pH of the natural rain. It took those seeds that were outdoors five days longer to germinate than those that were indoors. Of those plants that were sprayed with a pH 3.0 simulated acid rain, the ones indoors had visible damage to the outside of the cotyledons, the first leaf of the embryonic seed, while those that were outdoors had none. It was also noted that there was more damage to the seedlings kept outdoors. Caporn and Hutchinson (1987) also tested the effects of simulated acid rain at different temperatures: 10° and 20° Celsius. This research showed that the plants at higher temperatures were not as affected when compared to those at lower temperatures. In addition to environment and temperature, the authors tested the combined effects of simulated acid rain with a water shortage, as well as simulated acid rain with insufficient nutrients. In both cases, these tests revealed that the simulated acid rain caused less injury to those seedlings that were not given enough nutrients or water than to those that were given adequate amounts of either.To find out if the data that had been collected was statistically significant, the authors did an analysis of variance. This paper helped developed my hypothesis and my research proposal because the pH of the acid rain affected the cabbage seedlings, a vegetable, negatively. Although I am not using cabbage seedlings, I am, however, using a vegetable, snow peas and the effects may as well be negative.
Chen and Durbin(1994) studied the effects of pH on two species of marine phytoplankton. The pH range was 7.0 to 9.4. They adjusted the pH of the tanks using two different methods. The first method involved bubbling different types of compressed gases. These gases were CO2, compressed air, and a mixture of nitrogen and oxygen. Before the bubbling occurred, the pH was adjusted to a level of 8.9 by the addition of diluted NaOH. Then, it was split up into four different 1 L containers; three of them were bubbled with the compressed gases and the fourth was not. The three that were bubbled with CO2, compressed air, and a mixture of nitrogen and oxygen had resulting pH levels of 7, 8, and 9 respectively. The second method for adjusting the pH involved changing the pH by adding the necessary acid or base to obtain the desired levels of ranges 7.03 to 10.09. The authors do not specify which acids and bases were used to change the pH in the second method. The amount of photosynthesis that occurred was measured using in vivo fluorescence. This technique is a type of staining that can be used to see where and how many chemical reactions are taking place within a cell. Chen and Durbin (1994) found that the phytoplankton performed less photosynthesis at pH levels higher than 8.8. From this, a correlation was found between the high pH levels and the amount of carbon available. This research shows that there may be link between pH level and the amounts of photosynthesis a photosynthetic species can perform. The amount of photosynthesis may be altered due to the pH.
Bewtra et al. (1982) conducted an investigation to test reports that water hyacinths reduce the amount of pollution in lakes and rivers by decreasing the amounts of heavy metals. It was believed that if water hyacinths helped in rivers and lakes, then they could help reduce the pollution of the local landfills as well. Bewtra et al.(1982) studied how pH levels from landfill leachates affected the growth of water hyacinths. A landfill leachate is a toxic liquid that comes from water bubbling through a solid waste disposal site (Bewtra et al.,1982). This experiment was done in a greenhouse, and samples were taken from a local landfill in Ontario, Canada. The samples were high in chlorine and sodium, so they were diluted using tap water to concentrations that would be safe for the plants. This dilution was made using 20% leachate and 80% tap water. Ammonium nitrate and dipotassium hydrogen phosphate were also added to the dilution to serve as nutrients. Bewtra et al. (1982) added either sulfuric acid or potassium hydroxide to the leachate to obtain pH levels of 3.2, 3.4, 5.5, 6.5, 7.5, 9.0, 9.9, and 10.8. Two containers of water hyacinth were maintained at each pH level, as well as two for the pure diluted leachate, and two for tap water. They found that a pH below 4.0 and above 8.0 hindered the growth of the water hyacinth. They also found that the water hyacinth grew best between pH levels of 5.8-6.0. These results were helpful in the formulation of my hypothesis and methods section because it offered a different technique to change pH than was used in previous papers. Italso showed that there may be some scientific use to knowing different pH level tolerances for different plants such as reducing pollution.
Takemoto et al. (1988) studied the effects of acidic fog and ozone on green pepper crops in California. To start off the experiment, the plants were cultured in a greenhouse for 4 weeks before they were transferred to a location that was adjacent to the experimental site. The plants were allowed a 3 week adjustment period to get acclimated to the new conditions before they were randomly assigned to one of eight testing groups. These groups were then placed in open-top field chambers. Inside the chambers the plants were buried 0.22 m below the surface for root insulation. Fertilizer was applied weekly or water was added as needed. The open-top chambers were for fog chemistry/ air quality testing and the air quality was regulated using blowers that dispensed either charcoal-filtered or non-filtered air. The blowers were only run during the day and shut off at night to allow dew to form on the plant. Fog simulants were applied bi-weekly for eleven weeks using a fog application system. To make the fog solutions that were at pH levels of 2.6 and 1.6, the authors added HNO3 and H2SO4 in a 3:1 molar ratio. This ratio supplemented the amounts of NO3- and SO42- that were already in the simulants. The pH levels of the fog actually produced by the application system had pH levels of 1.68, 2.69, and 7.24 with standard deviations of 0.16, 0.17 and 0.27 respectively. They evaluated the visible injury to the plants after eleven fog treatments using a numerical scale of 0 to 4. Plants were assigned a score of zero if they had 0 to 5% injury, 1 if they had 5-25% injury, 2 if they had 26-50% injury, 3 if they had 51-75% injury and 4 if they had 76-100% injury. After the twenty second fog simulation the plants were harvested and separated into leaf and stem portions and then air dried for 5-10 days at a maximum temperature of 45°C. They used 2-way ANOVA tests to determine if the amount of injury to the different pH levels was significant or not. What they found was that while the plants in the fog pH levels of 2.69 and 7.24 were only 4-9% injured, those that were in the 1.68 fog pH group were injured 32 % with a standard deviation of 11.They also did tests on the amount of growth and yield that resulted from the different levels of pH and ambient O3 and found that a pH level of 1.68 hindered the growth and yield the most with those plantsgiving 3.8 fruits per plant on average compared to other numbers of 6.2, and 6.1.They found no significant interactions between fog pH and air quality (ambient O3levels). These results show that as mentioned earlier, there more than one type of acid deposition and this research shows the that it can be damaging to crop plants.
The effects of acid rain on epicuticular wax were investigated by Perce and Baker (1987). It has been noted that the amount of this wax is affected by the plants environmental surroundings such as temperature, wind, irradiance, and humidity. It has also been seen that erosion has occurred when the plants were subjected to a simulated acid rain (Percy and Baker, 1987). The authors of this research chose to look at four different species of plants; dwarf bean, field bean, pea and rape. All the seedlings were thirteen days old and grown in 10 cm pots with No. 1 compost. The plants were then placed in controlled environment chambers that provided the plant with a temperature of 20 – 15°C, a humidity of 75 – 85% and a photoperiod of 16 hours. There were twelve plants per pH group and the simulated acid rain was applied on alternate days over a 17 day period. The simulated rain treatments began as soon as the second initiated leaf pair emerged and they ended after the leaves were fully expanded. The pH of the treatments was changed using 1/1 M sulphuric/nitric acid to obtain pH levels of 4.6, 4.2, 3.8, 3.4, 3.0 and 2.6. The amounts of epicuticular wax were measured by washing the leaves of the plants with redistilled chloroform and then dried with anhydrous sodium sulfate. The solution was then filtered and evaporated and dried in pre-weighed vials. The wax was the only thing left in the vial and the weight was determined. The amount of surface area on a leave was also measured using an optomax series 1. Lesions were removed using fine tweezers and the surface areas were measured before and after their removal to determine the percentage of injury to the leaves. While leaf area of the dwarf bean was unaffected by the different pH levels, it was increased in the pea plant and decreased in both the rape and field bean. The four different plants were separated into two different categories of cuticle wax type; the first was crystalline wax, which appeared on the pea and rape plants, and the second was an amorphous wax, which was on the dwarf and field beans. The amorphous cuticle wax appeared to protect the leaves better than the crystalline. The dwarf and field beans only had lesions on the leaves of plants that were submitted to pH ≤ 3.0 and the pea and rape plants had lesions at pH ≤ 3.4. The plant with the most surface area injury was the rape with 4.4% of its surface area being injured and the least injured to the two bean plants with less than 1% being injured. That left the pea in the middle with 1.3% of its surface area injured. This is another study that shows that pH can affect plants. Specifically, it shows that pH can damage some important parts of a plant’s anatomy that help protect the plant and its structures.
My research tested the effects of different pH levels on pea plants. Snow peas,Pisum sativum, were chosen because they are easy to acquire, inexpensive, and can reach full maturity relatively quickly (Maynard and Hochmuth, 2007). While the peas were still seedlings they were watered with deionized water every other day until they sprout above the soil. Once the leaves had formed on allplants, watering with the solutions began.The solutions will be of different pH levels with 16 plants being watered at each pH. The pH levels I will use are 3.0, 4.5, 6.0, 7.0, 8.0, 9.5,and 11.0. This scale was chosen so that I can compare basic solutions with acidic solutions and determine which, if either, hasa more negative effect on the plants. The pH levels will be adjusted using sufficient amounts of either sulfuric acid or potassium hydroxide. My control for this experiment will be unaltered deionized water. I hypothesized that in general the plants watered with solutions of pH levels below 7.0 would grow better than those that were watered with levels above 7.0. The plants that were watered with solutions that are neutral or close to neutral such as tap water, deionized water, and a pH of 7.0 would have growth in-between those watered with the acidic and basic solutions. Furthermore, I specifically hypothesized that the pea plants would have the most growth and be the healthiest at a pH range of 5.0 - 6.0.These hypotheses were based on the previously mentioned research, as well as from the knowledge that peas grow best in acidic conditions (Maynard and Hochmuth, 2007).
Methods
Data Collection
I purchased approximately 200 snow pea (Pisum sativum) seeds and accelerated the growing process by germinating the seeds before planting them in the soil. The snow pea was chosen because it has a short maturation time period, easy to find, and relatively inexpensive which was essential in finishing my project in the time allotted and within budget.The germination was done by taking wet paper towels and placing them into 100 or 200 mL glass beakers. The seeds were then placed between the wet paper towels and the side of the beaker. Fifteen seeds were placed in each 100 mL beaker, while 50 were placed in each 200 mL beaker. Only 144 seeds were needed, so those that did not germinate or became moldy were discarded.