The Consequences of Nutrient Deficiencies in Tomato Plants
By Emily Burns
Abstract
During our investigation, we examined how different plant nutrient deficiencies affect growth and chlorophyll production of tomato plants. In order to explore this problem, we compared four nutrient treatments of plants, three with different nutrient deficiencies. We designated treatment one to be the control treatment. This treatment included complete nutrient availability. We designated treatment two to be nitrogen deficiency. We designated treatment three to be phosphorus deficiency. We designated treatment four to be distilled water. The plants were planted in a hydroponic recirculator. Based on the results after four weeks, we were able to conclude that only the standardized chlorophyll content in the phosphorus deficient plants was the same as the complete treatment after four weeks of growth. This verified our initial predictions prior to the experiment that essential plant nutrient deficiencies cause negative health effects concerning weight and standardized chlorophyll content with the exception that a phosphorus deficiency does not affect the production of chlorophyll in tomato plants. We were able to infer that chlorophyll production is not dependent on the availability of phosphorous.
Introduction
The plant nutrition experiment served the purpose to determine whether certain nutrient deficiencies in tomato plants would affect their weights and chlorophyll content after four weeks of being planted. According to Wilcox, 1994 tomato plants are easy to grow in a lab and their leaves show obvious sign of nutrient deficiency, which makes them ideal for experiments in nutrient deficiencies. The tomato plants in our experiment were young and in their vegetative growth stage. This stage in early tomato plant growth comes before the plant begins flowering and producing fruits.
Essential plant nutrients are minerals necessary for normal plant functioning and survival. Primary essential nutrients include nitrogen, phosphorus, and potassium. These macronutrients are usually limited in nature which can limit plant growth because plants need a large amount of these nutrients. Fertilizers compensate for the limited availability of these nutrients in the soil. For the plant nutrition experiment, we explored the effects of nitrogen and phosphorus deficiencies.
A nutrient deficiency causes negative health issues in most plants. These health issues can include a variety of symptoms which ultimately decrease quality of life as well as a plant’s fitness. Nutrient deficiencies involve both mobile elements and immobile elements depending on the nutrient. If a plant lacks a mobile nutrient, the effects of the deficiency will first appear on older leaves (Salisbury and Ross, 1992, p. 129). The younger leaves of the plant would appear green and healthy while the older leaves would yellow and wilt. If a plant lacks an immobile nutrient, the symptoms will appear first in young, new leaves. The nutrients used in this experiment are mobile elements: nitrogen and phosphorus.
Nitrogen occurs naturally as gas in the atmosphere and as an ion in the soil, usually as nitrate or ammonium. Nitrogen is an essential nutrient of most plants because it is found in proteins and nucleic acids. It is also needed for production of chlorophyll in plants. Plants with nitrogen deficiency experience many symptoms including yellowing of leaves and a shorter vegetative stage. The yellowing of leaves occurs mainly in older leaves. Also, although fruits are produced earlier in nitrogen deficient plants, the fruits tend to be smaller and of lesser quality (Salisbury and Ross, 1992, p. 130; Bennett, 1994). Plants are also effected hormonally by nitrogen deficiency. The absence of nitrogen in a plant’s diet inhibits the synthesis of cytokinin and quickens abscisic acid synthesis which causes the lifespan of the plant to rapidly reduce (Bergmann, 1992, p. 88).
Specifically, nitrogen deficiency in tomato plants tends to cause them to stand stiff and cause their stems to become hard and their leaves to reduce in size. The leaves yellow and ultimately fall off too early during the plants life. (Bergmann, 1992, p. 90). Chlorosis is more extreme between leaf veins in a plant experiencing early nitrogen deficiency.
The availability of phosphorus is limited in the soil. It is taken up by plant roots as the phosphate ion. Plants use phosphorus mainly for structural support in their membranes. In addition, phosphorus is an important nutrient for various metabolic roles, such as the phosphorylation of ATP as a source of energy for the plant during photosynthesis. A lack of phosphorus in a plant’s diet prevents many cellular functions. These can include reproduction of cells, maintaining metabolism, and inheritance of beneficial genes and traits (Salisbury and Ross, 1992, p. 131; Bennett 1994). Some plants can reutilize phosphorus from other sources, which increases transpiration rates, and survive for a period of time. This is not the case for tomato plants, however.
Tomato plants are sensitive to a phosphorus deficiency. According to Bergmann (1992, p. 98), in most plants, including tomato plants, phosphorus deficiency results in symptoms of stunted growth, curled leaflets, purple colored and thin stems, reduced production of fruit, yellowing of older leaves, and dark green colored young leaves. Young leaves appear darker in color and healthier because a lack of phosphorus prevents leaf growth but not the production of chlorophyll. Various cases of phosphorus deficiency causes the underside of leaves to appear purple due to the accumulation of purple anthocyanin pigment (Bergmann, 1992, p. 98).
A group of plants were grown in distilled water to test the effects of a complete lack of nutrients. Distilled water is water that has been boiled and stripped of its contaminants like inorganic minerals and metals through the process of distillation. The assumption is that plants grown in distilled water would be deficient of all nutrients (nitrogen, phosphorus, and iron); however, these plants mostly show the symptoms of nitrogen deficiency. They do tend to have subtle purple leaf veins, a symptom of a lack of phosphorus.
Standardized chlorophyll content is the amount of chlorophyll in milligrams per total leaf weight in grams. Plants with a high SCC would have dark green leaves and plants with a low SCC would have lighter colored green leaves. Measuring a plant’s SCC is a way to quantify the symptoms of nutrient deficiency.
My explanatory hypothesis states: Nitrogen and phosphorus are essential nutrients necessary for a plant to grow and survive. Based on this hypothesis, we made an initial prediction. We predicted that plants deprived of essential nutrients would show signs of unhealthy physiology and die. Also, we predicted that phosphorus deficient would maintain a standardized chlorophyll content similar to that of the complete treatment plants. We arrived at this prediction based on the thought that a lack of phosphorus does not affect production of chlorophyll in tomato plants. This experiment required the development of six null hypotheses for each deficiency in the context of weight change and change in standardized chlorophyll content as follows. The nitrogen deficient plants and the complete plants will have the same weights after four weeks of growth. The nitrogen deficient plants and the complete plants will have the same standardized chlorophyll content after four weeks of growth. The phosphorus deficient plants and the complete plants will have the same weights after four weeks of growth. The phosphorus deficient plants and the complete plants will have the same standardized chlorophyll content after four weeks of growth. The plants grown in distilled water and the complete plants will have the same weights after four weeks of growth. The plants grown in distilled water and the complete plants will have the same standardized chlorophyll content after four weeks of growth. Therefore, there are two research hypotheses for this experiment as follows. The nutrient deficient plants and the complete treatment plants will have different weights after four weeks of growth. The nutrient deficient plants and the complete treatment plants will have different standardized chlorophyll contents after four weeks of growth.
Materials and Methods
Two plants were used per group for each nutrient treatment. The plants were randomly selected to prevent bias and draw accurate conclusions. The purpose was to allow for any advantages or disadvantages unrelated to nutrient deficiency to be avoided because the experiment only served to analyze the effects of nutrient deficiency. The Plant Nutrition Deficiency OMP handout and procedures of Kosinski (2016) states the weighing procedures to follow in order to record initial weights of the plants before being planted and applied treatment. The procedure included removing and cleaning the soil from the plant’s roots and drying the plant to obtain the most accurate weights of the plants. This weight, in grams, was recorded.
The handout also states the procedures to follow in order to extract the chlorophyll from the leaves of the tomato plants to measure initial SCC. Each leaf blade was cut from the petioles of the first weighed plant and 5 grams of leaves were weighed out if possible. Using 15 mL of 90% acetone, the leaves were then crushed in a mortar. This mixture was transferred into a 50 mL beaker. A centrifuge tube was filled three-fourths full, approximately 10 mL, with the mixture in the beaker and then centrifuged at 2000 rpm for 5 minutes. The spectrometer should be warmed up at this point. After adjusting the wavelength to 663 nm, the absorbance of the extract was ready to be measured. The spectrometer was blanked using a cuvette filled three-fourths full of acetone, then then a cuvette of the chlorophyll extract and acetone mixture was filled and absorbance was measured. If the absorbance was over 1.00, the mixture was too dark for accurate reading, so it needed to be diluted. Any absorbance under 1.00 was recorded. To dilute the mixture of chlorophyll extract and acetone, a 1:9 ratio of mL of solution to mL of acetone was added to a graduated cylinder, mixed, and then piped into a new cuvette. The absorbance measured for the chlorophyll extract was used in the appropriate formula to calculate the initial standardized chlorophyll content.
The last procedure in the handout gave directions for planting the second plant in its designated hole in the hydroponic recirculator of a certain nutrient treatment. The steps of removing and cleaning the roots of the plant were repeated and the plant was placed in a plastic cup that was fitted into the hole with the plants hanging 2-3 cm below the base of the cup. To finish, the cup was filled with clay “Hydroton” pellets to keep the plant stable and upright and keep the interior of the recirculator dark. The location of the plant including the identification of the nutrient deficient recirculator was recorded for future reference.
The Procedures for Harvesting Tomatoes OMP handout of Kosinski (2016) states the directions for harvesting the tomato plants from their holes in the hydroponic recirculators after four weeks. The harvesting procedure required a repeat of the steps for cleaning the roots, drying them, and weighing the plant. If the plant was not obviously dead, the procedures for measuring the absorbance of the chlorophyll content was also repeated using 30 mL of 90% acetone and a twentyfold dilution instead of the initial tenfold. The final absorbance readings were used in their appropriate formulas presented in the lab handout to calculate the final SCC.
re…The treatments for this experiment were deficiencies of essential plant nutrients and a control using different groups of subjects for each treatment. Because of this, we can conclude that this data should be analyzed with an unpaired chi-square median test. Table 2 shows that the probability that the results in Table 1 happened by chance for all of the variables except for the final standardized chlorophyll content in the minus phosphorus treatment was less than 0.05, which is a high probability. So, we should fail to reject only the null hypothesis which states that the phosphorus deficient plants and the complete plants will have the same standardized chlorophyll content after four weeks.
Discussion
As shown in Table 1, on average, the weights of the plants in each nutrient deficient treatment were less than those of the complete treatment after four weeks. The average standardized chlorophyll contents of the plants were also less except for the phosphorus deficient treatment. The p-values, shown in Table 2, allow for conclusions to be drawn concerning the probability that the null hypotheses are true.
The p-value for the average final weight for the nitrogen deficiency treatment was approximately 0.0000015, which is a value much less than 0.05, so we have the evidence to reject the null hypothesis. The literature reports the effects of nitrogen deficiency in tomato plants that result in a reduced lifespan (Bergmann, 1992, p. 88). We saw these symptoms progressively worsen to the point of harvest. The nitrogen deficient plants showed obvious physical differences of color and health compared to the complete treatment plants. These nutrient deficient plants were much smaller in size and the leaves were yellow and wilted. This wilting and chlorosis of the plants resulted in very small final weights compared to the large weights of the plants grown in the complete treatment of nutrients. These results are shown in Table 1.
For the average standardized chlorophyll content for the nitrogen deficiency treatment, the p-value is approximately 0.00059, which is very low and less than 0.05, so we have the evidence to reject the null hypothesis. According to the literature, a lack of nitrogen in a tomato plant’s diet results in a reduced production of chlorophyll (Salisbury and Ross, 1992, p. 130: Bennett, 1994). We observed the chlorosis of the leaves in the experiment. The yellow color indicated the lack of green chlorophyll pigment. As shown in Table 1, the calculated standardized chlorophyll content for the nitrogen deficient plants was much lower than for the complete treatment. This is supported by the p-value.
The p-value for the average final weight for the phosphorus deficiency treatment is approximately 0.006, which is less than 0.05, so we have the evidence to reject the null hypothesis. Bergmann (1992, p. 103) reported that tomato plants are sensitive to a phosphorus deficiency. Observed lack of fruit production, dark green leaves with purple undersides, and stunted growth of the tomato plants in the phosphorus deficiency treatment provided confirmation of Bergmann’s claim and supported the p-value.
We initially predicted that standardized chlorophyll content in phosphorus deficient tomato plants would not be affected by the phosphorus deficiency. For the average standardized chlorophyll content for the phosphorus deficiency treatment, the p-value is approximately 0.49. Because this value is greater than 0.05, there is a high probability that the null hypothesis is true, so we do not have the evidence to reject the null hypothesis which states the phosphorus deficient plants and the complete plants will have the same standardized chlorophyll content after four weeks of growth. This conclusion proved our prediction and agrees with the scientific theory discussed in the literature. As reviewed by Roorda van Eysinga and Smilde (1981, p. 12), the tomato plants physiological aspect unaffected by a phosphorus deficiency is the intensity of the green color of the leaves. The leaves of phosphorus deficient plants in the experiment appeared only slightly darker green in color than the leaves of the control plants indicating a high concentration of chlorophyll. Although the average SCC for the phosphorus deficient plants was higher than the average SCC for the complete treatment, the difference was not significant enough to provide the evidence to reject the null hypothesis.
The p-value for the average final weight for the distilled water treatment was approximately 0.0000015, which is less than 0.05, so we have the evidence to reject the null hypothesis. The literature states that plants grown in distilled water would show mostly symptoms of nitrogen deficiency, including stunted growth. An initial observation of the distilled treatment plants for this experiment after four weeks of growth was the inferior size and necrosis of the plants compared to the complete plants. The weights of the plants were significantly different as well, hence the p-value. This data and observation agrees with the literature.
Finally, for the standardized chlorophyll content for the distilled water treatment, the probability that the null hypothesis is true is approximately 0.00059, which is less than 0.05, so we have the evidence to reject the null hypothesis. The plant leaves of the distilled water treatment showed extreme chlorosis, a major symptom of nitrogen deficiency and purple veins, a mild symptom of phosphorus deficiency, as reviewed in the literature. Yellow leaves lack the green chlorophyll pigment in the complete treatment leaves. Based on the compared SCCs, the p-value supports the claims in the literature.
One major problem during the experiment is that the data was ultimately biased and skewed. The averages were not as accurate as they should have been; they were too low to guarantee accurate conclusions to be made. The final data for complete plants in one section of data is missing from the table because the absorbance of the leaf/acetone mixture was too high and resources were discarded before the procedure could be repeated and corrected.
In addition, many of the complete treatment plants fell over a week prior to harvesting. All essential nutrients were available to the plants grown in this treatment, so plant growth was not limited and the plants grew to be very big and healthy. Fortunately, the plants that fell over survived and we were able to collect enough weights and determine standardized chlorophyll content to analyze the hypotheses.
For future experiments, a few changes could be made to better the validity of the experiment. Either a shorter experiment period or better support for the plants in the complete treatment would prevent them from becoming too heavy and falling over to avoid any errors. Also, to prevent such extreme variation and bias in the data, it would be beneficial to start with slightly larger plants more equal in size and similar quality during the initial investigation week. Overall, the results from the experiment were obvious almost the best they could possibly be. Accurate conclusions could be drawn with no difficultly.