Growth Responses to Nitrogen in Three Species - Research Paper Example

Growth responses to nitrogen in three species Name Institution Introduction Growth response to nutrients especially nitrogen differs greatly among different plant species. In a study on plant responses to nutrients, Shipley and Keddy (1998, p. 56) observed the growth of 28 plant species fertilized with 1/10 strength and full-strength Hoagland’s solution. The growth response to the varying nutrient supply differed greatly among the different plant species. For instance, RGR (relative growth rate) increased for species that received a high nutrient treatment by 11 percent for those with the least response and 850 percent for those with the highest response. Many other studies carried out on the subject have also shown significant differences in the level to which growth in different plant species is stimulated by nutrients. Such variation in growth response among plant species can be a crucial determinant of distribution of plant species across natural fertility gradients. The ability of a species to respond to additional nutrients with increase in growth is an important aspect of success in fertile environments. Plant species which occur naturally in fertile environments have a bigger growth response to nutrients as compared to species in less fertile habitats. The aims of this experiment are to compare and contrast the growth dynamics of three species which are corn, barley, and pea using indices such as relative growth rate and to determine the effect of availability of nitrogen on the growth and development of the three plant species. Materials and methods Materials Seeds of corn (Zea mays), Barley (Hordeum vulgare) and field pea (Pisum sativum) Plastic pots Paper bags Methods Corn (Zea mays cv. SR73), barley (Hordeumvulgarecv. Schooner) and field peas (Pisumsativum) were sown on the 2nd March 2014 into trays of seed raising mix (Debco). After 6 days, seedlings of similar size and developmental stage were selected and sown into pots of soil - sand (1:4) mix, watered and placed in the Glasshouse Complex. The pots were labeled with the group number and the kind of treatment to be imposed in each pot. After the second practical (Mar 12-13) when initial measurements were taken, plants were watered three times a week with modified Hoagland solution containing 16 mM NO3- and 8 mM NH4+ (+ N) or no NO3- and no NH4+ (no N). Enough nutrient solution was applied to ensure the soil - sand mix remained moist but little remained in the trays by the end of the watering period. On March 21, several corn plants in the + N treatment began showing symptoms of nitrogen deficiency (yellowing of the first leaf). The amount of nutrient solution applied was doubled but two days later the first leaves of most corn plants were yellowing. As these observations indicated a low N status (and a problem with the nutrient solution used), the + N plants were then watered with Aquasol® (Hortico) (1.6g/L, containing 0.3 mM MAP, 1.5 mM KNO3and 5.3 mM Urea) for one week and with double-strength Aquasol® for the remainder of the experiment. Experiment design For each nutrient treatment and species, there were three replicate trays containing 5 pots each (15 in total). Measurements during practical Two of the plants that were to be grown to the final harvest had a number of measurements taken. These measurements included the shoot height, number of leaves, developmental stage, number of branches or tillers, and the stem length. One of the plants was removed from the pot and the same parameters measured. The roots were removed from the shoot and for the peas the number of active nodules was taken. The root materials were stored into a paper to dry. Leaves from the plant were also separated from the stem and both the leaves and stems placed in separate bags. All the bags were labeled with plant species, date, plant part, and group number. The results were entered onto the data collection sheet. At the final harvest, the measurements which were taken at the start were also taken at this stage. Results After 21 days of growth, there were a number of observations that were made on the three plant species. For corn, the plants that were treated with nitrogen had a larger leaf area as compared to those that did not receive any nitrogen treatment. This was also observed in barley and pea. However, the difference in the leaf area was more pronounced in corn and barley, with the leaf area for those plants treated with nitrogen being almost twice the leaf area of those that did not receive nitrogen treatment, as compared to field pea. After 35 days, corn and barley plants that had received nitrogen treatment had bigger leaf areas as compared to those that had not received the nitrogen treatment. However, the difference between the two areas was reduced as compared to the one observed after 21 days. For pea, the leaf area for those plants that had not received nitrogen treatment was bigger than for the ones that had received nitrogen treatment. Measurements also provided varying results for each group of plants. After 21 days, the measurement of the shoot dry mass showed that corn plants that had been treated with nitrogen had a higher shoot dry mass as compared to the ones that did not receive nitrogen treatment. Similar results were observed in pea and barley plants. For root dry matter, measurement results indicated that the root dry matter reduced with nitrogen treatment. Plants that did not receive nitrogen treatment had a bigger root dry mass as compared the ones that received nitrogen treatment. The net assimilation rate increased with nitrogen treatment for 21 days of growth for all plant species. However, the rate decreased for 35 days of growth. The leaf area ratio also varied among the three species. For corn and pea, the LAR was lower for the plants that had been treated with nitrogen as compared to those that had not received nitrogen treatment for 21 days of growth. For barley, the plants that had been treated with nitrogen had a larger LAR. Similar results were obtained for 35 days of growth. The specific leaf area for all the plants was lower for the plants treated with nitrogen in 21 days of growth. For 35 days of growth, the specific leaf area was higher in plants treated with nitrogen for corn and barley. For pea, the SLA was also lower in plants treated with nitrogen. Figure 1: Shoot dry weight Figure 1 shows the growth response of the shoot of the plants with nitrogen treatment. From the graphs, it can be observed that corn had the largest growth response as compared to barley and pea when treated with nitrogen. Pea, on the other hand, had the least growth response. The growth response in barley was also influenced by the tiller number. The tiller numbers used were 2.3 for plants treated with nitrogen and 0.5 those not treated with nitrogen. Figure 2: Leaf area Figure 2 shows the growth response of the leaf of the three plants with nitrogen treatment. From the graph, it can be observed that growth response in terms of leaf area increases with nitrogen treatment for all the three species. Figure 3: DM partitioning to roots Figure 3 shows the growth response of the three plants in terms of dry matter partitioning to roots. From the graph, it is observed that dry matter partitioning to roots reduced with nitrogen treatment. Very few nodules were observed on the roots of the field peas. Figure 4: Relative growth rate Figure 4 shows the change in the relative growth rate of the three species with nitrogen treatment. It is observed that there is a general increase in relative growth rate with nitrogen treatment. Figure 5: Leaf area ratio Figure 5 shows the change in the leaf area ratio with nitrogen treatment. For corn and barley, the leaf area ratio reduces with nitrogen treatment. For barley, the leaf area ratio increases slightly with nitrogen. Figure 6: Net assimilation rate Figure 6 shows the net assimilation rate for the three species with nitrogen treatment. It is observed that there is a general increase in the net assimilation rate with nitrogen treatment. Figure 7: Specific leaf area Figure 7 shows change in the specific leaf with nitrogen treatment. It is observed that there is a general reduction in the specific leaf area for the three species with nitrogen treatment, although the reduction is very slight in pea plant. Discussion From the results, it can be deduced that the three plant species have a high growth response to the supply of nitrogen. This is observed in the changes that occur in the plants when they are supplied with nitrogen as compared to the ones which are not provided with nitrogen. Effects of nitrogen to shoot and root growth From the results, it can be observed that nitrogen has a positive effect on the growth of plant shoot in the three species. This is seen in the growth difference between plants which were treated with nitrogen and those which were not treated with nitrogen. The growth in the shoot of the plants with increase in nitrogen supply can be attributed to the function of nitrogen in cell growth and development. Almost all compounds which take part in cell growth, metabolism contain nitrogen. Therefore reduced amount of nitrogen results to a reduced rate of growth. Increase in nitrogen in these plants therefore resulted in increased cell growth and tissue development in the shoot of the plants resulting in an increase in the overall growth of the shoot. This explains the growth difference between the plants that were treated with nitrogen and those that were not. For roots, increase in the level of nitrogen reduced growth of the roots of the plants. This is because most of the nitrogen absorbed by the roots moves up the shoot. This leaves the roots with little to rely on for growth. The results also indicate increased nitrogen leads to increased growth of the leaf area. Like in the shoot, nitrogen is also responsible for the development of various structures and substances in the leaves such as chloroplasts and chlorophyll. Deficiency of nitrogen results to underdevelopment of these structures. This reduces the leaf area of the affected plants. On the other hand, increased supply of nitrogen results to increase in the leaf area because of the development of the various leaf structures. Effects of nitrogen on relative growth rate From the results, it can be seen that increase in nitrogen supply results to increased growth rate in the three species. The increased growth rate can be attributed to increased cell division and growth in the plants due to presence of nitrogen. Nitrogen is responsible for the formation of amino acids which take part in the formation of various plant tissues and organs. The increased level of nitrogen means that the rate of formation of the organs increases. This results to the overall increase in the rate of growth of the plant. Effect of nitrogen on leaf-area ratio It is observed, from the results, that the leaf area ratio reduces with increase in nitrogen. The leaf area ratio reduces because of the increase in the leaf area due to high level of nitrogen. Nitrogen results to the increased growth rate of the leaves in the plants. As such, the leaf area increases. Presence of nitrogen in the plants also increases the dry weight of leaves. The increased dry weight therefore leads to reduced leaf-area ratio. Effect of nitrogen net assimilation rate and specific leaf ratio The results from the study show that there is a general increase in the net assimilation rate. This is due to increased rate of photosynthesis which provides the plants with food to grow. Nitrogen is responsible for the formation of chlorophyll and chloroplast in plants. Therefore an increase in the amount of nitrogen in the plant results to increased level of chloroplasts and chlorophyll. The increased amount of these two substances results to increased rate of photosynthesis. This in turn leads to increased growth. Consequently, the net assimilation rate increases. The specific leaf ratio reduces with increase in nitrogen treatment. This is due to increase in the dry weight of the plants with due to presence of nitrogen. With increased cell growth and development due to availability of nitrogen, dry weight of the plants increased. This therefore led to a reduction in the specific leaf ratio which is determined by dividing the photosynthetic surface area by dry weight. Conclusion Nitrogen is a crucial component to plants in terms of growth. Most plants depend on nitrogen and deficiency in nitrogen results to impairment in growth for many plants. Different plant species respond differently to nitrogen. The aim of this experiment was to compare the growth dynamics of three species which are field pea, corn and barley when treated with nitrogen. From the experiment, it was found that the three species responded differently to nitrogen in terms of the level of growth. However, they showed generally similar characteristics. For instance, all the species showed in an increase in relative growth rate, net assimilation rate, leaf area, and shoot dry weight and a reduction in root dry weight and specific leaf ratio when treated with nitrogen. Bibliography Sinclair, T. R., & Vadez, V 2002 ‘Physiological traits for crop yield improvement in low N and P environments’, Plant and Soil, vol. 245, no.1, pp. 1-15. Andrews, M., Sprent, J. I., Raven, J. A., & Eady, P. E 1999 ‘Relationships between shoot to root ratio, growth and leaf soluble protein concentration of Pisum sativum, Phaseolus vulgaris and Triticum aestivum under different nutrient deficiencies’, Plant Cell and Environment, vol. 22, pp. 949-958. Fichtner, K., & Schulze, E. D1992 ‘The effect of nitrogen nutrition on growth and biomass partitioning of annual plants originating from habitats of different nitrogen availability’, Oecologia, vol. 92, no. 2, pp. 236-241 Taub, D. 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