Effect of Temperature on Leaf Decay - Lab Report Example

PAGE EFFECT OF TEMPERATURE ON LEAF DECAY Decomposition is a natural process where plant and animal organic matter is broken down into small particles .it is a crucial link in food chains and food webs because they return to the soil organic compounds that enhance plant growth. Decomposition of leaves is a stepwise process, which involves. 1. Fragmentation: - where solid particles are broken down into smaller fragments by which the surface area for microbial action increases. 2. Leaching: - it is a process where rainwater percolates into the plant material dissolves and carries away the nutrition. 3. Mixing: - where soil material and plant material along with moisture get mixed either due to movement of organisms like earthworms, wind, rain etc. The factors that affect the rate of leaf decay are. 1. Organisms: -bacteria and fungi are the most common organisms causing decomposition of organic matter. They digest the organic matter by use of enzymes and derive nutrition from it for their growth and multiplication .these organisms are also called saprophytes. fungi release enzyme cellulase which is major carbohydrate in plants and is decay resistant. 2. Temperature: - saprophytes work faster at warmer temperature. If temperature is too high or too low saprophytes cannot grow and rate of decomposition is slow. Microbial activity generally predicted to increase rapidly up to a temperature of 30 degree C. an optimal temperature for microbial activity is between 35 to 45 degree C. 3. Moisture: - increases the rate of decomposition. 4. Air: - most saprophytes use oxygen in air to cause decay. 5. Chemical composition: - i9ncreased nitrogen content of leaves will cause an increase in the decay of leaves as it is more utilized by fungi and the rate gets faster. Agar: - it is a phycocolloid extracted from red purple marine algae, which belong to class rhodophyceae. Agar is a gel at room temperature and remains firm at as high as 65 degree C. Nutrient agar will grow the largest number of different types of microbes fungi and bacteria. Nutrient is beef broth plus yeast. Beech (fagus): - belongs to the family fagaceae. Leaves are entirely or sparsely toothed, 5 - 15 cms long and 4- 10 cm broad. Rate of decomposition is faster due to low lignin content, which is a decay resistant. Decay of leaves can be estimated by the change in 1. Their mass 2. Quality (which is calculated as ratio of C: N of decayed dry material. 3. Their chemical content. 4. Changes in soil or water, which act as medium. 5. Linear wave equation Wt = Wo - Kt where Wt = mass observed after specific time period, Wo = initial weight, K = decay constant. PAGE 2 PREDICTION Rate of decomposition will increase with increase in temperature and will be negligible at very high and very low temperatures. METHOD Agar jelly and mini-petri dishes were used. The agar had no feed in it. It was only used as a Base to keep the leaf circles in place. The leaf circles would act as food for the microbes to Grow on. To test different temperatures 5C, 20C, 30C and 65C were used. In each dish 10 leaf circles were put . Each leaf circle had a diameter of 5mm. To make sure that this experiment was safe, the lid was cello taped and wasn't opened till the experiment was over . The leaf circles were then observed during a 4-week period. Any change in size of the leaf Material could be measured. Graph paper was put behind each petri dish when measuring. Dishes were put into the following positions for each temperature A - 5C - Refrigerator B - 20C - Laboratory bench C - 30C - Incubator D- 65C - Incubator Beech leaves were chosen for the experiment as they rot quickly. The experiment would have taken years if Holly would have been used instead, as this does not rot quickly. Results During the experiment It was found that the leaf circles did not appear to reduce in size. Fungus grew around some of the circles, the diameter of the circle plus fungus through the weeks was measured to establish the temperature effect .the following data was obtained and Compiled into tables. PAGE 3 Weeks/dia(mm) 1 2 3 4 5 6 7 8 9 10 Start 5 5 5 5 5 5 5 5 5 5 1 week 5 5 5 5 5 5 5 5 5 5 2 weeks 5 5 5 5 5 5 5 5 5 5 3 weeks 5 5 5 5 5 5 5 5 5 5 4 weeks 5 5 5 5 5 5 5 5 5 5 TABLE 1 : Diameter of leaves and fungus at 5 degree C in all the 10 dishes over period of 4 weeks Weeks/dishes 1 2 3 4 5 6 7 8 9 10 Start 5 5 5 5 5 5 5 5 5 5 1 week 7 6 7 7 7 7 7 7 8 8 2 weeks 9 8 9 9 10 12 9 9 9 10 3 weeks 12 12 12 12 13 12 10 10 10 11 4 weeks 16 16 16 12 12 17 16 14 14 14 TABLE 2 : Diameter of leaves and fungus at 20 degree C in all the 10 dishes over period of 4 weeks Weeks/dishes 1 2 3 4 5 6 7 8 9 10 Start 5 5 5 5 5 5 5 5 5 5 1 week 9 9 9 8 10 9 9 9 8 9 2 weeks 13 13 13 13 12 12 12 12 12 14 3 weeks 18 18 18 18 17 14 16 16 16 20 4 weeks 22 22 24 25 20 24 24 24 23 22 TABLE 3: Diameter of leaves and fungus at 30 degree C in all the 10 dishes over period of 4 weeks Weeks/dishes 1 2 3 4 5 6 7 8 9 10 Start 5 5 5 5 5 5 5 5 5 5 1 week 5 5 5 5 5 5 5 5 5 5 2 weeks 5 5 5 5 5 5 5 5 5 5 3 weeks 5 5 5 5 5 5 5 5 5 5 4 weeks 5 5 5 5 5 5 5 5 5 5 TABLE 4 : Diameter of leaves and fungus at 65 degree C in all the 10 dishes over period of 4 weeks PAGE 4 Where 1 = 5 degree C series 2 = start 2 = 20 degree C series 3 = week 1 3 = 30 degree C series 4 = week 2 4 = 65 degree C series 5 = week 3 Series 6 = week 4 INTERPRETATION Based on the results above it can be said that decomposition at extreme high and extreme low temperatures is zero and the decay process increases with increase in temperature as depicted in the temperature vs. mean diameter graph. There is minimal or no microbial activity at extreme temperatures. There fore the process of decay is slow at such temperatures. Decaying process tends to be faster at warmer temperatures as it facilitates microbial growth therefore as the temperature increases the decayi9ng process also increases. Thus the results are very much similar to our prediction. PAGE 5 DRAW BACKS OF EXPERIMENT 1. CONTROLS: - no controls were used in the experiment. So artifacts or contamination cannot be ruled out. 2. VARIANCE: - In this experiment temperature should have been the only variant and rest of the factors like light, moisture be kept constant. 3. LIGHT: -all the specimens should have been kept in dark. Now we cannot make out if the diff in decay was due to difference in temperature or diff in light. 4. AIR: this is another parameter that should have been kept constant. Now we cannot make out if the difference in decay was due to difference in temperature or due to aerobic or anaerobic bacteria. 5. DIAMETER: decay process is not uniform it is not necessary that decay starts from the margin it may start from center also. In such condition calculating the diameter is erroneous. 6. ERRORS: the changes recorded in first week and 2nd week may be due to contamination or dampening due to moisture and such early changes doesn't occur. 7. NUMBER OF OBSERVATIONS: Adequate numbers of observations were not made. Instead of increasing the number of dishes to 10, less number of dishes should have been used and observations made at more frequent temperatures so that optimal temperature could be calculated, 8. EQUIPMENT: placing leaves in agar jelly and petre dishes has slowed the process and limited the process of decaying, as less surface area is accessed. Instead nutrient agar should have been used in bottles. 9. ANAMOLOUS RESULTS: there were many anomalous results; these may be due to wrong calculation of diameter or environment variation. Such anomalous can be neglected specially when such large numbers of specimens are being used. METHODS TO IMPROVE EXPERIMENT 1. CONTROLS: appropriate use of controls. Controls should be taken at optimum decaying temperature between 35 to 40 degree C. 2. VARIANCE: temperature should be the only variant. The agar, moisture should be kept constant. 3. LIGHT: all specimens should be kept in dark or optimum light. 4. AIR: all specimens should be kept airtight. 5. MASS: instead of diameter the mass of the leaves should have been taken into amount because tissue on decay loses mass and there is no question of uniformity. And the exact rate of decomposition could be made out for proper analysis. 6. CHEMICAL COMPOSITION: the carbon and nitrogen estimation of the decaying plant product would give us valuable information about the quality of the decaying leaf. 7. FURTHER STUDY: the pH, electrical conductivity, and dissolved oxygen concentration of the water should be measured with portable digital potentiometers. The plant material should be ground in preparation to determine nitrogen concentration (Kjeldahl digestion) and total phosphorus concentration PAGE 6 (spectrophotometry) (Allen et al., 1974). Leaf quality to be assessed by the C:N ratio, calculated as percentage C divided by percentage N of the dry mass. REFERENCES 1. ANDERSON, J. M., 1973, The breakdown and decomposition of sweet chestnut (Castanea sativa Mill.) and beech (Fagus silvatica L.) leaf litter in two deciduous woodland soils II. Changes in the carbon, hydrogen and polyphenol content. Oecologia, 12: 275-288. 2. AYYAPPAN, S., OLH, J., RAGHAVAN, S. L. & SINHA, V. R. P., 1986, Macrophyte decomposition in two tropical lakes. Arch. Hydrobiol., 106: 219-231. 3. BOULTON, A. J. & BOON, P. I., 1991, A review of methodology used to measure leaf litter decomposition in lotic environments: time to turn over an old leaf Aust. J. Mar. Fresh. Res., 42: 1-43. 4. IVERSEN, T. M., 1975, Disappearance of autumn shed beech leaves placed in bags in small streams. Verh. Internat. Verein. Limnol., 19: 1687-1692. 5. - 5. Dickinson, C. H. and G. J. F. Pugh. 1974. Biology of plant litter decomposition. 2 volumes. Academic Press, New York. ISBN 0-1221-5001. 6. Swift, M. J., O. W. Heal, J. M. Anderson. 1979. Decomposition in terrestrial ecosystems. Studies in Ecology. Vol. 5. Blackwell, Oxford. Read More