Introduction
- The decaying process is the final step in the lifecycle of leaves. The step that leads to leaf decay is the process of the leaf falling off the tree. Chlorophyll is food for leaves, and once the tree stops producing chlorophyll the leaf falls off the tree. Chlorophyll is what keeps leaves green and healthy. Chlorophyll absorbs both violet and red light which causes the leaf to reflect green wavelengths of light. Chlorophyll masks many colors in leaves like the color carotene. When leaves fall off the trees their chlorophyll is depleted and colors like carotene are able to be seen in the leaf. When leaves start to loose chlorophyll they start to become brittle and decay. The green chlorophyll that is produced in the summer overpowers the other chlorophyll that the leaf produces, therefore as the green chlorophyll breaks down the other chlorophyll is made visible because it is a different color. Eventually the leaf will turn brown because of the loss of all the chlorophyll. Right before leaf fall, the protective layor of the leaf is waterproofed and strengthened, and the separation layer swells and becomes gelatinous. Due to this information our group should see a loss of chlorophyll in the leaves through the process of leaf decay. Since the protective layer is waterproofed we have concluded in our hypothesis that the leaves in water will decay the slowest, and the leaves in nothing will decay the quickest. Oxygen is necessary for decomposition and the leaves left open to the air should decay the qickest. Due to the leaves waterproofing layer the water will not effect it that quickly, and when the leaves are in dirt or on dirt the dirt will act as a protectant. We believe the leaves in nothing will decay the quickest because there is nothing to preserve them and they are exposed to the air all of the time, therefore the oxygen will affect them more quickly.
Materials and Methods
-Red maple leaves
-dirt
-water
-containers
-wire mesh
-sunlight (greenhouse)
-scale
-camera
- First, our group gathered 160 red maple leaves and a bucket of dirt. We then weighed and labeled each leaf individually. Next, we set up 16 containers in the green house. Four containers contained nothing, four contained water, and eight contained dirt. We placed ten leaves in each container. So in total there were forty leaves in four empty containers, forty leaves in four containers filled with only water, forty leaves on dirt in four containers, and forty leaves in dirt in four containers. Next, we placed wire mesh over the containers with plain leaves, and the leaves on the dirt in order to keep them from blowing away. For our experiment we will check each week and see the stages of the leaves over four weeks. We will weigh each leaf (in grams) and describe the leaves as a whole from each of the environments. We will also take pictures each week in order to have good observation records. Each week we will take away one container in each group to account for the stages of leaf decay. We will save the leaves once we take them away and save them in the science center, just to be on the safe side.
Class Involvement
- After explaining our lab and our weight measurements to the class, we will split the group into their different lab groups (i.e. the spiders, the sediment people). We will then have the groups do our comparisons for us. We will give each group our measurements that we did on every leaf at the beginning of the lab, plus give them the measurements we did in one week. We will then have them compare the groups, comparing the means of the weights of each week for each leaf environment. We will have them make a histogram for each leaf environment comparing the two weeks. This will help them compare the means. Then we will have them decide the rate of decay by comparing the weight changes between one of the leaf environments. We will have the groups record this data, and one person from our group will join each of the other groups to help them do their comparing, and to make sure they are doing the right comparisons.
Analysis
- We will analyze the weight loss and the color change from the first week through the fourth week. Because we weighed the leaves before we started the experiment, we will be able to tell how much the leaves have deteriorated from week to week when we weigh them again. From week to week we will be able to tell color change and texture differences because we will compare the pictures we take of the leaves. We will also see the different rates of deterioration among the groups: water, on dirt, in dirt, and with nothing. Our group will use statview and super Anova to compare data results.
Thanks to Wal-Mart's photo processing, we were unable to analyze our pictures we took of the leaves each week, so we were unable to report the changes in appearance. However, upon looking at our data, we discovered that it was necessary to calculate percentage weight loss instead of just weight loss. We could not compare the weight loss because all the leaves did not start out at the same weight. In fact, we ran a T-Test comparing the initial weights of the different leaves and received a P-Value of .0001, proving that the initial weights were significantly different between leaves. However, the percentage of weight loss is basically the same for nothing, in dirt, and on dirt. This was proven due to the T-test results. For this T-test we received a p-value of .7658, which leads us to conclude that there is no signifigant difference between the weight loss due to the different environments. On the second T-test we ran which compared the leaves percent weight loss in nothing, in dirt, and on dirt over the four week period we received the p-value of .0729. This also states that the weight loss were not signifigantly different. We did not use our data from the environment of in water because we did not dry our leaves before we weighted them. In neglecting to do this, our weights showed that the leaves actually gained weight each week. If we were to include this data into our T-Test comparisons, it would definitly have shown that the percentage weight loss was significantly different, and we would not know if this was the reason for that particular conclusion, or if there were other difference as well. We did compare the percentage weight loss that was calculated over the four weeks for the leaves in water, and we found that they steadily gained weight. However, we cannot say for sure if the leaf steadily lost mass, which led it to absorb more water, or if it simply absorbed more water.
To answer our question, we can say, from analyzing our data, that the weight loss of a leaf after it falls off of a tree is not signigicantly affected by if it lands in dirt, on dirt, or on nothing. We can also say that if a leaf was to fall into water, it would steadily gain weight, if a person were to pick it right out of the water and weight it, without drying it out.
Bibliography
-Bell, Ritchie C. and Lindsey, Anne H.. Fall Color and Woodland Harvests. Laurel Hill Press, Chapel Hill, N.C. 1990. Pg. 3-4, 94.
-Encyclopedia Americana 1995 ed. Vol. 17. "Leaf." Pg.108-109.
-How to Make Compost. http://www.dep.state.pa.us/dep/deputate/airwaste/wm/RECYCLE/FACTS/compost.htm
-Ketchum, Richard M.. The Secret Life of the Forest. American Heritage Press, New York 1970.
-Leaf Colors. http://oldblue.umeche.maine.edu/leaves.html
-Platt, Rutherford. 1001 Questions Answered About Trees. Dodd, Mead and Company, New York 1959. Pg. 8,86.
-World Book Encyclopedia 1997 ed. Vol. 12 "Leaf." Pg. 152,153.
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