Macronutrient Malnutrition in Tomato Plants ABSTRACT Plants need a variety of mineral elements readily abundant in their soil for proper growth and development. Consequently, deficiency in one of these elements often has deteriorating effects on plants. In this lab, tomatoes were hydroponically grown in different deficiency mediums and observed throughout the course of four weeks. The deficiency effects of nitrogen, phosphorus, and distilled water were observed and the plant weight and SCC were computed. All of the treatments affected plant development and showed significance difference from the complete, except for the SCC of the distilled water. INTRODUCTION Plants require large amounts of macronutrients such as carbon, phosphorus, and nitrogen, and trace amounts of micronutrients such as chlorine and iron in their medium for proper development (Solomon 2011). Natural soil and plant tissues are very complex and are known to contain over 60 elements, 19 of which are essential for growth (Solomon 2011). Deficiencies in these minerals lead to many deteriorating effects on plants including chlorosis, necrotic spotting, and drying of their leaves (Helms 1998). If the symptoms become visible on older leaves first, the mineral is known as a mobile element; it has the ability to leave older tissues and migrate to newer tissues (Kosinski 2015). The two minerals studied in this experiment, nitrogen and phosphorus, are considered mobile elements. An immobile element, such as iron, localizes its damaging effects on terminal growth and younger leaves (Helms 1998). Nitrogen is an essential component of nucleic acids, proteins, chlorophyll, and various plant hormones (Solomon 2011). However, because plants must absorb the element in the form of fixed nitrogen, it is the most commonly deficient component in soil. Nitrogen deficiency in plants can result in stunted growth as well as yellowing and drying of the lower leaves (Kosinski 2015). Phosphorus is another macronutrient in soil. In plants, it plays a role in energy metabolism and is a fundamental element in nucleic acids, coenzymes, and phospholipids. If a plant is deficient of this essential mineral, resulting symptoms may include purple-­‐tinted, narrowed leaves, and inhibited growth (Helms 1998). The tomato leaves appear dark in phosphorus-­‐deficient treatments because chlorophyll synthesis is not inhibited but leaf growth is (Kosinski 2015). Since natural soil is so complex, an experiment observing the deficiency of one element is hard to monitor and must be done by a different method. Hydroponics is a useful technique supplying plants with nutrients through liquid environments. The system consists of an air pump, which allows roots to respire and take up nutrients present in the medium (Solomon 2011). In this experiment, tomato plants were observed during their vegetative growth period for four weeks. The tomatoes were grown hydroponically in complete, distilled water, nitrogen deficient, and phosphorus deficient mediums. The increased biomass in tomatoes during this stage of development is largely from the leaves (Kosinski 2015). The resulting effects were observed and compared using the average plant biomass and standardized chlorophyll content (SCC) for each treatment. The complete medium served as the positive control and contained all necessary macronutrients and micronutrients for growth. The distilled water treatment was the negative control and the tomato plants were not expected to grow. In a 2004 study, nitrogen deficiency significantly reduced the leaf chlorophyll content and biomass of sorghum plants (Zhao 2004). Therefore, I hypothesized that the plant weight and SCC value in the nitrogen-­‐deficient treatment would be lower than in the complete. The null hypotheses propose that these values are the same for both mediums. Nadira (2014) observed notable differences in biomass, organic acid secretion, ATPase activity, and carbohydrate metabolism in wild barley grains when grown in differing phosphorus mediums. Mineral deficiencies are also known to cause a difference in biomass, notably in the root system of plants (Hermans 2006). These findings led to my hypothesis that the plant biomass and chlorophyll content would be different in the phosphorus medium than in the complete. The null hypothesis states that the final weight and SCC will be the same for both. Even though the distilled water treatment lacks all other nutrients needed for development, the resulting symptoms are most similar to nitrogen deficiency (Kosinski 2015). The expected chlorosis and stunting of growth led me to hypothesis that there would be a difference in plant weight and SCC when comparing the negative and positive controls. The null hypotheses state that these observed values are the same for both treatments. MATERIALS AND METHODS The main concepts of this procedure were taken from the Biology in the Laboratory manual experiment 30E (Helms 1998) and edited into an OMP (Kosinski 2015). On March 10-­‐12, 2015, the weight and standardized chlorophyll content (SCC) of a random set of tomatoes was determined in order to obtain initial values. Then, a second set of plants were prepped and set up in hydroponic recirculators. They were randomly planted in either a complete, distilled water, nitrogen-­‐deficient, or phosphorus-­‐deficient medium. Every week, the visible differences and development progress of the plants were noted. On April 7-­‐9, 2015, the tomato plants were harvested following the specific instructions in the OMP (Kosinski 2015). All of the class’s data was compiled in order to find the average plant biomass and SCC observed in each of the mediums. The results of the nutrient-­‐deficient treatments were then compared to the complete in order to note any statistical differences. An un-­‐paired chi-­‐square test was used for all six comparisons because the control used different tomato plants than the other treatments. RESULTS Table 1. Mean value of Plant Weight (g) for each Treatment Complete DH2O -­‐N -­‐P Initial 13.8 15.0 16.8 10.1 Final 70.7 20.4 32.3 42.5 Final Weight (g) Effect of Treatment on Plant Weight 80 60 40 20 0 Complete DH2O −N −P Treatment Figure 1. Effect of Treatments on Plant Weight. The nutrient deficient treatments in comparison with the complete based on average final weight, measured in g. Table 2. Statistical Analysis of Plant Weight dH20 -­‐N -­‐P Chi-­‐Sq 16.7 15.6 7.8 P value 4.36E-­‐05 7.71E-­‐05 0.0052 Table 3. Mean value of SCC (mg/g) for each Treatment Complete DH2O -­‐N -­‐P Initial 0.244 0.211 0.19 0.22 Final 0.735 0.329 0.364 0.152 SCC (mg/g) Effect of Treatment on SCC 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 Complete DH2O −N −P Treatment Figure 2. Effect of Treatment on SCC. All of the nutrient deficient treatments in comparison with the complete based on mean SCC, measured in mg/g. Table 4. Statistical Analysis of SCC dH20 -­‐N -­‐P Chi-­‐Sq 1.24 6.33 12.9 P value 0.265 0.012 3.26E-­‐04 After 2 weeks, the plants growing in the complete medium towered over the others, nearly hitting the overhead lights. The plants in distilled water were growing the slowest and were only a third of the size of the complete plants. Deficiency symptoms were first visible three weeks into the experiment. The -­‐P plants looked very thin but were towering over the plants in distilled water. Chlorosis was visible on the leaves of the nitrogen-­‐
deficient plants. On harvest week, a notable amount of plants in the complete treatment had fallen over because the roots clogged the hydroponic system. Table 1 shows an increase in average plant weight for each of the four treatments. The final weights for the nutrient deficient treatments were compared to the complete treatment’s final weight of 70.7g. These relationships are shown in Figure 1; the distilled water treatment hindered growth the most. The deficiency treatment was compared to the control through an un-­‐paired chi-­‐square test. The chi-­‐square value represents the statistical difference and results in a probability (p value) that measures significance. If the p value is less than 0.05, the null hypothesis is rejected. Therefore, a p value greater than 0.05 indicates that there is no significant difference between treatments and the null hypothesis cannot be rejected. The p values for the distilled water, nitrogen deficient, and phosphorus deficient treatments are 4.36*10-­‐5, 7.71*10-­‐5, 0.0052, respectively (Table 2). The initial and final mean values for SCC are shown in Table 1; each treatment increased SCC except for the nitrogen deficient. The final SCC value for each nutrient deficient treatment was compared to the final SCC value of the complete treatment, 0.735 mg/g. Figure 2 shows that the phosphorus deficient treatment affected SCC more than the distilled water or nitrogen deficient treatment. Statistical analysis of the SCC final means is shown in Table 4. The p values for the dH2O, -­‐N, and -­‐P treatments were 0.265, 0.012, and 3.26*10-­‐4, respectively. DISCUSSION Figure 1 shows that the average plant weight decreased in all of the nutrient-­‐
deficient treatments compared to the complete. After performing an unpaired chi-­‐square test, the p values for each treatment were less than 0.05. This gives statistical evidence to reject the null hypothesis that there is no difference. This data was expected since mineral deficiencies are known to cause stunting effects on plants (Zhao 2005; Nadira 2014). The chlorophyll content of the nitrogen-­‐deficient and phosphorus-­‐deficient treatments were compared to the complete and resulted in p values of 0.012 and 3.26*10-­‐4, respectively. Since these values are significantly small, the null hypotheses must be rejected. This supports my original hypotheses that these values would be different because nitrogen deficiency results in yellowing of leaves (Kosinski 2015) and phosphorus deficiency causes a purple-­‐tint (Helms 1998). However, the observed SCC in the distilled water treatment resulted in a large p value of 0.265, which does not provide enough significance to note any difference. This disproves my original hypothesis since I expected to observe deficiencies symptoms similar to nitrogen (Kosinski 2015). It should be noted that by the end of the four weeks, many of the plants in the complete treatment had completely fallen over. Roots had clogged up the system and inhibited growth; the plants had simply gotten too big. This could have been prevented if we had started the experiment with smaller, younger plants. Starting with younger plants would have also allowed deficiency symptoms to be more visible (Kosinski 2015). In addition, since the plants were sectioned in different parts of the room based on treatment, error could have occurred if there were any defects with the lights. A more random method of planting would eliminate this potential error. The physiological effects of nutrient deficiency in plants are well known but how the plant goes about responding to these changes is still in question. Studies are now beginning to focus on the signaling cascades of plants (Hermans 2006). This knowledge would allow for more efficient use of minerals and new approaches for sustainable agriculture. LITERATURE CITED Helms, D. R., C. W. Helms, R. J. Kosinski and J. R. Cummings. 1998. Biology in the Laboratory, 3rd Ed. W. H. Freeman and Co., New York, p. 30:8-­‐14. Hermans, C., J. Hammond, P. White, and N. Verbruggen. 2006. "How Do Plants Respond to Nutrient Shortage by Biomass Allocation?" Trends in Plant Science 11.12: 610-­‐17. Kosinski, R. J. 2015. A literature review on nutrient deficiencies in tomatoes. Web site at http://people.clemson.edu/~rjksn/111/nutrient.htm. Kosinski, R. J. 2015. Plant Nutrient Deficiency. Biology 1111 Lab OMP, Clemson University. Kosinski, R. J. 2015. Procedures for Harvesting Tomatoes. Biology 1111 Lab OMP, Clemson University. Nadira, U. A., I. M. Ahmed, J. Zeng, N. Bibi, S. Cai, F. Wu, and G. Zhang. 2014. "The Changes in Physiological and Biochemical Traits of Tibetan Wild and Cultivated Barley in Response to Low Phosphorus Stress." Soil Science and Plant Nutrition: 1-­‐11. Solomon, E.P. Martin, C. E. Martin, D.W. Berg, L.R. 2011. Biology 10 Ed. The Soil Environment. Cengage Learning, CT. pp. 767-­‐773. Zhao, D., K. R. Reddy, V. G. Kakani, and V. Reddy. 2005. "Nitrogen Deficiency Effects on Plant Growth, Leaf Photosynthesis, and Hyperspectral Reflectance Properties of Sorghum." European Journal of Agronomy 22.4: 391-­‐403.