Abstract
The literature stated that nutrient deficiencies should effect the weight and chlorophyll content of tomato plants. In this experiment, four treatments were used to determine the effects of nutrient deficiencies. The first treatment was the control group of plants which were grown in a complete medium that contained no deficiencies. The second treatment was a group of plants grown in distilled water. The third treatment was a group of tomato plants grown in a medium lacking nitrogen. The fourth treatment of plants was grown in a medium without phosphorus. These plants were grown for four weeks until they were analyzed. The average final weight for the complete plant was 39.0937 grams which was significantly higher than the weights of the second, third, and fourth treatments, which were respectively 2.75 grams, 3.6777 grams, and 7.4333 grams. The average final standardized chlorophyll content of the distilled water was 0.2350 and the final average for the nitrogen deficient plants was 0.3035. Those values were significantly lower than the average final value for the complete plants which was 0.7901. The medium lacking phosphorus had a final average standardized chlorophyll content of 1.1220 which was significantly greater than the complete medium. These values supported the relationship between deficiencies and plants.
Introduction
This experiment was performed in order to determine whether nutrient deficiencies have an effect on the weight and standardized chlorophyll content of tomato plants. We determined the effect of nutrient deficiencies by evaluating and examining three different deficiencies. The first treatment was the complete experiment. This treatment did not contain any deficiencies. For the second treatment, distilled water was used. For this treatment, we evaluated plants when both nitrogen and phosphorus were deficient. In the third treatment, the tomato plants were nitrogen deficient. The effects of a phosphorus deficiency were evaluated in treatment four.
According to the literature, nutrient deficiencies are defined as a lack or shortage of one or more nutrient. These deficiencies can lead to many issues and has several effects on plants. Stunted growth is a type of growth failure that can be caused by nutrient deficiencies. Chlorosis and necrosis are also some known effects of nutrient deficiencies. Chlorosis is the yellowing of a plant while necrosis is the death of a plant. According to Salisbury and Ross (1989), if mobile elements are missing the effects are seen in the older tissue first (Salisbury and Ross, 1992, p.129). This occurs because a plant extracts elements from its older tissues and then sends those elements to the newer tissue. This will cause older leaves to appear more yellow and wilted while the newer leaves are green. If an immobile element is deficient, the new tissue will be affected first because the plant cannot withdraw the elements from older tissues.
Lycopersicon esculentum, also known as tomatoes, show very obvious symptoms of nutrient deficiencies. The different growth stages of these plants require different nutrients. The plants that are forty to seventy days old are considered young. This stage of the young plants is called the vegetative growth stage. This means they have not begun flowering and producing their fruit. In this stage, most of the increase in mass occurs in the leaves. When the tomato plants are at harvest, most of the plant’s mass comes from the fruit that it produces. These plants require high amounts of nutrients. One of the most important nutrients that they require is phosphorus. (Wilcox, 1994)
Nitrogen must be fixed into an inorganic compound in order for it to be useable by plants, therefore, nitrogen is commonly the most deficient element in soils. According to Bergmann (1992), around one to five percent of a plant’s weight comes from nitrogen (Bergmann, 1992, p. 86). The most common effect that a plant experiences during nitrogen deficiency is stunted growth. This occurs because nitrogen plays a huge part in proteins and nucleic acids. It also plays a role in many macromolecules. The yellowing of a plant’s older leaves is another known effect of nitrogen deficiency. This color change occurs because, in order for chlorophyll formation to occur, nitrogen must be present (Salisbury and Ross, 1992, p. 130; Bennett, 1994). When the nitrogen is not present, the newer leaves withdraw the nutrients from its older tissues since nitrogen is a mobile element.
Nitrogen deficiency can also impede vegetative growth and quicken flowering. The reasoning behind this is that this deficiency places many hormonal effects within the plant. These effects cause a change in cytokinin and abscisic acid synthesis. It causes the synthesis of abscisic acid to accelerate while slowing the synthesis of cytokinin, therefore, aging the plant more quickly. This increase in the speed of aging causes the lifespan of the plant to become reduced (Bergmann, 1992, p. 88). Overall, tomato plants with a deficiency in nitrogen tend to have small yellow leaves and thin stems.
A plant takes in phosphorus as phosphate ions and it is the commonly the second most nutrient deficiency in plants. Phosphorus is important in plants because it is used in the phospholipids within the membranes. It also plays an important role in things like DNA, RNA, and ATP. A deficiency in phosphorus leads to problems in cell reproduction, metabolism, and inheritance. Some plants are capable of recycling phosphorus when there is no more available. This can lead to higher respiration rates in those plants. A deficiency in phosphorus can retard leaf growth but does not affect chlorophyll synthesis. Therefore, plants suffering from phosphorus deficiencies have leaves that are darker green in comparison to the leaves of a plant that is not suffering from this deficiency. According to Bergmann (1992), this darker coloration makes this deficiency more difficult to spot without the use of a control plant. Tomato plants tend to suffer from phosphorus deficiencies by showing symptoms like darkening of young leaves, yellowing of old leaves, thinning of stems, purple coloration of leaf veins, and lower amounts of fruit production. (Bergmann, 1992, p. 103)
When a plant is grown using distilled water, it is considered nutrient deficient because distilled water is lacking nutrients. Therefore, the plant is deficient in nitrogen and phosphorus. Since nitrogen plays a greater role in a plant, a plant suffering from nitrogen and phosphorus deficiencies tends to show more symptoms of a nitrogen deficiency than phosphorus. This especially occurs when a plant cannot grow in the absence of nitrogen because the plant’s need for the other nutrients is reduced. The plants in distilled water can also tend to have a purple coloration on their veins as a result of the phosphorus deficiency.
The explanatory hypothesis for this experiment states that nitrogen and phosphorus are essential elements that are needed for plants to grow. This hypothesis was used to predict the outcome of this experiment. The prediction for this experiment was that nutrient deficiencies would affect the weights and standardized chlorophyll contents after four weeks of growth. There were two research hypotheses for this experiment. The first was that the weights of the nutrient deficient plants would be different that the weights of the complete plants after four weeks of growth. The second research hypothesis was that the plants with a nutrient deficiency would have a different standardized chlorophyll content compared to the complete plants.
The research hypotheses lead to the development of six different null hypotheses. The first null hypothesis is that the plants grown in the distilled water will have the same weights as the plants grown in the complete medium. The second null hypothesis is that the plants grown in the medium lacking nitrogen will have the same weights as the plants grown in the complete medium. The third null hypothesis is that the plants grown in the complete medium and the plants grown in the medium lacking phosphorus will have the same weights. The forth null hypothesis is that the plants in the complete medium will have the same standardized chlorophyll content as the plants grown in the distilled water. The fifth null hypothesis is that the plants grown in the medium lacking nitrogen will have the same standardized chlorophyll content and the plants in the complete medium. The sixth null hypothesis is that the plants grown in the complete medium and the plants grown in the medium lacking phosphorus. During this experiment, the independent variable was the determined deficiencies. The controlled variable was that the amount of plants used per deficiency were the same.
Materials and Methods
Using the procedures given in the lab handout of Kosinski (Plant, 2016), we evaluated and prepared the plants for the experiment. To begin we turned on the spectrophotometer to allow it to warm up. Then each group randomly selected two tomato plants and removed the soil by shaking and washing the roots in water. Next, the plants were patted dry and weighed using a scale and the value was recorded. Then all the leaf blades of one plant for each group were cut off and weighed. Those values were recorded as well. If the mass of the leaves was less than five grams, all the leaves were used for the next part of the experiment. If the mass was greater than five grams then five grams of leaves were randomly selected.
The five grams of leaves were then placed into a mortar along with fifteen milliliters of 90% acetone. The leaves were crushed by rolling the pestle over the leaves fifty times. This mixture was then poured into a fifty-milliliter beaker. Then the mixture was poured into a centrifuge until it was filled about three-fourths full. The tube was then centrifuged at 2000 rpm for five minutes. After the centrifuge was complete, the absorbance was read at 663 nanometers. To read the absorbance, the wavelength had to be set to the correct value. Then the blank was made by filling a cuvette with acetone. The blank was placed into the holder while ensuring the triangle at the top of the cuvette was facing towards us. The lid was closed and the “0 ABS” button was pressed. Then another cuvette was filled with the chlorophyll extract and the absorbance was read. If the absorbance was over one, the content had to be diluted by mixing one milliliter of chlorophyll content with ten milliliters of acetone and then the absorbance was reevaluated by filling another cuvette with the new mixture. The absorbance was then recorded and the standardized chlorophyll content was determined by using the appropriate formula.
The other plants were then planted in a hydroponic recirculator. First, the black plastic cups were cleaned and then the roots of the tomato plants were looped through the holes in the cups. The cups were then filled with hydroton pellets in order to help the plant stand upright. The cups were then placed into their assigned hole of the hydroponic system.
After four weeks the plants were removed from the hydroponic system by following the procedures given in the lab handout Kosinski (Procedures, 2016). To begin, the spectrophotometer was turned on. Then the plants were removed from their respective pots and the pellets were dumped out. The roots were then patted dry and the same procedures were followed in order to determine the mass. To determine the standardized chlorophyll content, thirty milliliters of acetone was placed into a mortar with the leaves and the mixture was diluted by placing half a milliliter of the solution into a graduated cylinder with nine and a half milliliters of acetone. The same procedures were then followed to determine the standardized chlorophyll content.
The weights and standardized chlorophyll contents for each plant for each treatment were recorded and averaged as indicated in Table 1. Using the date given, we performed an unpaired analysis test because the experiment used multiple independent subjects. The average values were used to determine the chi-squared and p-values for each treatment as indicated in Table 2.
Discussion
As shown in Table 1, there was a difference in weight and standardized chlorophyll content between the complete treatment and the treatments with a deficiency. This difference was significant enough to prove that nutrient deficiencies have an effect on tomato plants. However, this did not apply to the standardized chlorophyll content of the medium lacking phosphorus. The average SCC of these tomato plants was higher than the average for the complete tomato plants. Since the P-value for this treatment was greater than five percent, we failed to reject the null hypothesis. Also, since the Chi-squared value was considerably low, there was a high probability that the null hypothesis was true. According to the literature, this data was correct because a plant suffering from a phosphorus deficiency should not experience an effect on chlorophyll synthesis. In our experiment, these plants looked much darker than the ones grown in distilled water. This occurred because a phosphorus deficiency leads to the accumulation of purple pigments within the leaves.
According to the literature, a plant grown in distilled water should experience stunted growth. This is true because these plants will express the symptoms of a nitrogen deficient plant and those plants are commonly known to be affected in growth. In this treatment, we observed the treatments before they were harvested. At that time, they were smaller than plants grown in the complete medium. The data indicated in Table 1 corresponds to the literature because the P-value, as indicated in Table 2, was less than five percent which allowed us to reject the null hypothesis. The Chi-squared value for this treatment was high, therefore, there was a low probability that the null hypothesis was true.
As stated above, a deficiency in nitrogen leads to stunted growth because of nitrogen’s role in proteins, nucleic acids, and other macromolecules. Therefore, in comparison to a plant without any deficiencies, a nitrogen deficient plant should have a lower weight. Our data helped support the literature since our P-value allowed us to reject the null hypothesis. Our observations before harvest were that these plants were much smaller and fragile that the complete plants. Our data concluded that tomatoes suffer from nitrogen deficiency in the form of stunted growth.
Our initial prediction for tomato plants suffering from a phosphorus deficiency was that the weights after four weeks of growth would not be the same as the weights of the complete plants. According to the data in Table 1, there was a decrease in the average weight for these deficient plants in comparison to the control group. Since the P-value was 0.0059, we were able to conclude that the difference in weights was significant enough to reject the null hypothesis and prove that the literature was correct. These plants, right before harvest, were significantly shorter than the complete plants. Our data and observations helped prove that this deficiency leads to issues in cell reproduction, metabolism, and inheritance, therefore, leading to stunted growth.
The literature stated that plants grown in distilled water express most of the same symptoms as those grown in a medium lacking nitrogen because nitrogen is a vital nutrient for the plant. Therefore, since nitrogen deficient plants suffer from chlorosis, so should plants grown in distilled water. Our data proved this theory correct because the standardized chlorophyll content for the distilled water medium tomato plants was significantly lower than the nutrient containing plants. This difference was great enough to prove the theory right because the P-value was less than five percent. Although the leaves in this treatment suffered from chlorosis, they also experienced some purple coloration within their veins. The SCC data and observations corresponding to the nitrogen deficient plants also suggested chlorosis. The leaves of these plants were small and yellow. The null hypothesis for the nitrogen deficient plants was also rejected according to the P-value indicated in Table 2.
Although our data supported the literature, many errors could have occurred. One of the most important problems that occurred was that the complete treatment plants fell over when they got big, therefore, the data for that treatment could have contained some error. Another issue within this experiment was that the starting plants were very small. This means that the plants with a deficiency did not have enough starting nutrients to withdraw from, therefore, leading to more extreme results and symptoms. There was a bias within this experiment because of the varying sizes of the plants. There was a large cap between the weights of the largest and smallest plants within the complete treatment, therefore, creating an issue with the averages. The variation in these values can affect the chi-squared test because it can make it the results seem non-significant. Many changes should be made in the future investigations for this experiment. Some of those changes could include a larger test group with a smaller variation in order to have a more accurate and precise average. Also, next time the experiment could go for less time in order to prevent the complete plants from growing too large for the units. This change will allow for more accurate results. Another change for a future experiment could include evaluating the weight and standardized chlorophyll content after each week in order to determine the effect of nutrient deficiencies over time.
2016-4-22-1461286963