The effect of phosphorus concentration on the growth of Salvinia minima Chesa Ramacciotti

Transcription

1 Ramacciotti 1 The effect of phosphorus concentration on the growth of Salvinia minima Chesa Ramacciotti I. Introduction The aquatic plant species Salvinia minima and Lemna minor have been known to absorb nutrients such as phosphorus and nitrogen when in contaminated waterways. This process of absorption could possibly be used in the future of phytoremediation, a method of removing pollutants from various soil and water environments. 1 In order to assess whether this procedure will be successful in the future, relative growth rates of the different species alone and with contaminates need to be examined. Salvinia minima is a floating water fern located mainly in the Southern United States; it can also be found in parts of New York, Massachusetts, and Maryland. 2 In New York, the water fern is listed as exploitably vulnerable, which means it is in danger of being eliminated because of human causes. In Florida, North Carolina, and Texas most of the Salvinia genus is listed as a noxious weed, sans the S. minima species. 3 In this experiment, the growth rates of Salvinia minima were to be observed both with and without the addition of phosphorus. In Experiment 1, cultures were set up with varying starting population sizes to assess growth rates and as a control for other experiments. For Experiment 2, the effect of added KH2PO4 on Salvinia minima growth was measured. Replicates of this experiment were completed in order to obtain more data and receive a more precise measurement. In the first experiment, it was expected that the culture with the larger starting size would have a faster rate of increase but both cultures would be sustained at similar carrying capacities. In the

2 Ramacciotti 2 second experiment, it was expected that the cultures that contain phosphorus would have a faster rate of increase than those grown without the nutrient. II. Materials and Methods In Experiment 1 of this procedure, two cultures were set up to identify the growth rates of Salvinia minima plants. In the first culture, 12 plants were added to an artificial pond water bath in a 1 oz. plastic container. A plant was defined as one stem, even if it had multiple thalli, which were the leaves on the plants. In the second culture, 24 individual plants were added. In Experiment 2, three cultures of 24 plants each were prepared according to the instructions above. In addition, 2 ml of concentrated KH2PO4 was added to each culture. The population size, measured in number of thalli, was recorded over a five week time period to identify growth rates of the species. In other groups experiments, the effect of phosphorus and nitrogen were tested on Salvinia minima and Lemna minor species individually. Competition between the two species was also tested experimentally. All of these procedures came from the Bio 22W Lab Protocol Manual. 1 Experimental Design Experiment 1: 12 Salvinia Plants 24 Salvinia Plants Experiment 2: 24 Salvinia Plants + KH2PO4 24 Salvinia Plants + KH2PO4 24 Salvinia Plants + KH2PO4

3 Ramacciotti 3 The plant cultures were kept in the greenhouse from February 24 through March 31, 214. The greenhouse was maintained at approximately 7ºF in a sunny atmosphere during the day with darkness at night. The plants were watered every Monday, Wednesday, and Friday while the weekly counts took place on Monday afternoons. Every Monday, 2 ml of the concentrated KH2PO4 was also added to the three experimental plant cultures. Some algal growth was seen in each of the cultures starting around the fourth week of the experimental period. In addition, small black flies were seen on all of the plant cultures in the last week of the experimental time frame. Once counts were taken, analyses were drawn using population growth equations. Exponential growth is modeled by the equation: dn = r dt maxn, where dn dt is the change in number of individuals in the population over the change in time, r is the maximum per capita rate of increase, and N is the number of individuals in the population. Geometric rate of increase (λ) can be related to the maximum per capita rate of increase by the equation: λ = e r or N t+1 N t = λ. The logistic growth curve is described by the equation: dn = r dt maxn [1 N ], where K is the carrying capacity of the K population. The carrying capacity can also be estimated by the area of container divided by the area of an average thalli leaf. The Lotka-Volterra Competition model was used by the group investigating competition. This can be described as: dn dt = r 1 N 1 [ K 1 N 1 N 2 ], where N1 and N2 correspond to the population size of two different K 1 species, K1 is the carrying capacity of species one, r1 is the rate of increase of species one, and is the competition coefficient of the effect of species two on species one. 1

4 N (Population Size-Number of Thalli Ramacciotti 4 III. Results Experiment 1: Each week, the population counts were taken based on the number of thalli present in each plant culture. In the tables below, the population counts are recorded, separated based on experimental design. Plant Culture Number of Thalli Day Day 14 Day 21 Day 28 1 (Starting pop 12) (Starting pop 24) Table 1: Growth of Salvinia minima (Experiment 1-Phyto Fighters) Plant Culture Number of Thalli Day Day 14 Day 21 Day 28 1 (Starting pop 12) (Starting pop 24) Table 2: Growth of Salvinia minima (Experiment 1- #SalviniaProbz) 3 Average Growth Rates for Salvinia minima of various starting Population Sizes Time (Days) Starting Pop 12 Starting Pop 24 Graph 1: Average growth of Salvinia minima at various starting populations

5 ln(n) ln(n) Ramacciotti 5 Approximation of r (intrinsic rate of increase): 6 Approximation of r for Starting Population Size 12 5 y =.656x Time (Days) Graph 2: The approximation of r using ln(n) vs time for starting population 12 Approximation of r for Starting Population Size y =.552x Time (Days) Graph 3: The approximation of r using ln(n) vs time for starting population 24 The approximation of r is the slope of the line of ln(n) vs. time. For the starting population size of 12, the approximation of r was.656 while the for the starting population size of 24 it was.552.

6 Geometric Rate of Increase (λ) Geometric Rate of Increase (λ) Ramacciotti 6 Geometric Population Growth Rate (λ): Plant Culture Value of λ ( N t+1 ) N t Day to Day 14 Day 14 to Day 21 Day 21 to Day 28 1 (Starting Pop 12) (Starting Pop 24) Table 3: Geometric growth rate values for individual time intervals (From Experiment 1) Estimation of K, Carrying Capacity: 1. Based on Surface area: K=589mm 2 /28mm 2 = Salvinia 2. Based on Geometric Rate of Increase: 3 Estimation of K for Starting Population Size y = -.85x N Population Size 2.5 Graph 4: Estimation of K with starting population size 12 Estimation of K for Starting Population Size 24 2 y = -.2x N Population Size Graph 5: Estimation of K with starting population size 24 K is the point as which λ = 1. Based on the equations, K is 2 for the starting population of 12 and 523 for the starting population of 24.

7 N (Average Population Size in Number of Thalli) Ramacciotti 7 Experiment 2: Plant Culture Number of Thalli Day Day 14 Day 21 Day Table 4: Growth of Salvinia minima with the addition of Phosphorus (KH2PO4) (Experiment 2- PhytoFighters) In the following graph, the population growth data for Salvinia minima with the addition of phosphorus is displayed. The data for each of the three cultures was averaged for the different days that counts were taken. 3 Population Growth Data for Salvinia minima with the affect of Phosphorus concentration y = e.535x y = e.552x Time (Days) With Phosphorous Control Expon. (With Phosphorous) Expon. (Control) Graph 6: Growth of Salvinia minima with added Phosphorous

8 Geometric Rate of Increase Ramacciotti 8 Value of λ ( N t+1 ) Plant Culture N t Day to Day 14 Day 14 to Day 21 Day 21 to Day 28 Experimental Average Table 5: Geometric growth rate values for individual time intervals (From Experiment 2) 2.5 Estimation of K with Addition of Phosphorous y = -.58x N Population Size Graph 7: Estimation of K of Salvinia minima with added phosphorous Based on the graph above, the estimation of K for Salvinia minima with the addition of phosphorus in 283 thalli. IV. Discussion Overall, the hypothesis in this experiment was not entirely supported. In Experiment 1, the starting population of 24 had a slower rate of increase than the starting population of 12. In Experiment 2, the growth of the Salvinia minima plants with the addition of phosphorous was slightly faster than the growth of the plants without the nutrient. Thus, the addition of KH2PO4 had an effect on the growth on Salvinia minima. This means the plant could be useful in phytoremediation efforts

9 Ramacciotti 9 that require the absorption of nutrients from various bodies of water because plant growth was affected by nutrient addition. The hypothesis was not supported in the fact that the carrying capacities for the variations in Experiment 1 differed greatly. This could have had to do with the growth rate values and the averaging of two groups data. The numbers greatly varied between groups which could have affected the value obtained for the carrying capacity. Among all experiments, the Lemna minor plants had a faster growth rate than the Salvinia minima plants. In the Lemna minor experiments, the value of lambda decreased continuously throughout the time frame. However, in the Salvinia minima experiments, the value of lambda first decreased then increased in the last time interval. Nitrogen seemed to have a bigger effect on the growth rates of Salvinia while phosphorous had a larger effect on the growth of Lemna. Based on this information, the particular plants could be used in different phytoremediation efforts. In the competition experiment, Salvinia minima proved to be the better competitor over Lemna minor. Based on this information, Salvinia would seem to outcompete Lemna when they are grown together and could therefore be the more suited plant in short term phytoremediation situations. With every experiment, there are chances of errors occurring which could affect the data received. In this experiment, algal growth began to become a problem around the fourth week of data collection. The growth of algae in the plant cultures could have affected the growth of the Salvinia minima plants. If the algae was not present, the growth of the Salvinia would have most likely increased. Another source of error

10 Ramacciotti 1 was the collection of data, specifically counting the thalli. Because there was such excessive growth in the plant cultures, it was sometimes difficult to count each individual thalli, especially those that were found under the initial layer of growth. This small estimation could have affected the overall results received. In short, before either Salvinia minima or Lemna minor are used in any phytoremediation efforts, more experimentation needs to be completed. Tests should be done in order to see how well the plants actually take up the nutrient or how well they grow in the long term in bigger settings. Experiments could be completed in order to determine the amount of nutrient each plant can uptake and its resulting growth. Also, experiments could be done to determine how Salvinia and Lemna grow in various environmental locations and how well they survive long term. In general, the information gathered through this experiment is useful in initially determining growth of Salvinia minima and Lemna minor, but more should be done before these plants are used in wide scale phytoremediation efforts. V. References 1 Hass, C.A., D. Burpee, R. Meisel, and A. Ward A Preliminary Study of the Effects of Excess Nutrients and Interspecies Competition on Population Growth of Lemna minor and Salvinia minima In a Laboratory Manual for Biology 22W: Populations and Communities. (Burpee, D. and C. Hass, eds.) Department of Biology, The Pennsylvania State University, University Park, PA. Adapted from Beiswenger, J. M Experiments to Teach Ecology. A Project of the Education Committee of the Ecological Society of America. Ecological Society of America, Tempe, AZ. pp "Salvinia minima." Plantpedia. Aquascaping World, 29. Web. 16 Apr < nt=water%2spangles>. 3 Plants Profile for Salvinia minima (Water spangles). United States Department of Agriculture: Natural Resources Conservation Service. Retrieved March 3, 214, from