Our lab group has decided to discover what factors determine the rate of change in the color and losing of honeysuckle leaves. The green pigment present in leaves, chlorophyll, wears out and is lost as the weather cools with the increased nighttime. As the chlorophyll abundance decreases with the cooler days and shortened daylight hours, other pigments that are always present can now be seen. We are going to conduct several different experiments to find out which factor, daylight or temperature, affect the leaves color more. We plan to do this by covering several plants with a clear garbage bag and a dark garbage bag. This test will compare the affects of hours of daylight received by the branches. We will also be taking saplings out of the ground and placing them into a greenhouse. This test will determine how much temperature affects the changing and losing of leaves by trees. We are hoping that cooler temperatures that will be present in these two tests will accelerate the process of foliation and color transformation of the leaves therefore forcing them to drop from the branches sooner.
We believe that environmental factors like, temperature and day length, play major roles in the color change in leaves and rate that they fall and that:
a. Artificially shorter days will accelerate the rate that the leaves change color and fall.
b. Warmer temperature will reduce the rate this change occurs. And a frost will increase the rate that this change occurs.
In one recent project, researched in the fall of 2000, was done on the rate of color change on oak trees in Oxford. We are going to expand on this topic and study why oak trees change and what factors play into the change. We have done some research to support our idea that temperature and day length both play a role in the seasonal change trees go through.
The entire food supply of trees lies in the most visible part of the tree, the leaf. It is inside of these leaves where chemical reactions occur in order to feed the entire organism. Chlorophyll, a green pigment, is the most dominant pigment being the reason why leaves are most commonly green.
With the coming of the fall season, the days get shorter and the temperatures begin to drop considerably in the transition from summer to winter. Trees notice this change in the calendar as the daylight hours decrease as well as the intensity of the sunlight and prepare themselves for the harsh winter season. With fall coming, trees gradually slow the food making processes until eventually the process stops. As photosynthesis decreases, the chlorophyll begins to break down and leave the plant cells and be re-absorbed by the tree (www.sciam.com/askexpert/environment18.html). This allows for the other pigments to be visible. The mixture of the chlorophyll and other pigments, such as carotenoids and anthocyanins, results in the different colors seen in the leaves during autumn time (www.ces.ncsu.edu).
The yellow color is the result of yellow orange and red pigments known as carotenoids. These carotenoids are a vital supply of Vitamin A in plants. When found in flowers and the like they are used to attract pollinating insects. In trees they aid in the conversion of sunlight to sugar energy. Red, Blue, and Violet colors are the result of anthocyanins. These are not contained but are distributed randomly throughout cells. The acidity of the cell determines the color. These pigments will dissolve water which is why if you boil red leaves the water turns red (www.nps.gov/blri/flowers.htm ). The shutting down of food making causes fluid carrying veins inside of each leaf to cut off its supply to the leaves, which trap extra sugars in the leaf (www.accuweather.com).
Physical changes also occur in the tree during this transformation. A layer of cells begin to develop along the leaf's base and cut into the leaf in order to pry it loose from the branch. The cut in the branch is soon sealed therefore causing the leaf to become released from the tree and fall to the ground.
The physical and chemical appearances of the trees have three main factors for these changes: pigments, length of night, and weather. These factors directly affect the features that will be visible in the leaves of a tree. Different pigments are more dominant in some species of tree and, therefore, are better seen in that specific species than another. For instance, oak tree leaves generally turn red or brown before tumbling down to the earth, while aspen and yellow poplar trees turn a golden yellow tint (www.accuweather.com). Factors in the tree's environment also affect possible features of the tree. If trees are generally exposed to a period of warm, sunny days and then proceeded by cooler nights, the sugars produced during the day are trapped, allowing the non-dominant pigments to show through more clearly (www.ces.ncsu.edu).
One problem plants face when the temperature of the environment falls is a change in the fluidity of cell membranes. When a membrane cools below a critical point, it loses its fluidity as the lipids become locked into crystalline structures. Rapid chilling is generally more stressful to plants than a more gradual drop in air temperature. Oaks, maples, roses and other woody plants native to regions where winters are cold have special adaptations that enable them to cope with freezing stress (Campbell 765). Another article (www.enn.com/enn-newsarchive/1999/09/090299/drfoilage_5414.asp)
talks about the effect that stress such as drought and ice-storms have on the colors of trees. The drought in New England in 1999 made the trees change early due to lack of water. It also says that trees "inherit" fall colors. It depends on how much magnesium, iron, phosphorus and sodium is in the tree as well as the acidity of the chemicals in the tree’s leaves.
Ch. 39 of the Campbell book also talks about the control of daily and seasonal responses. Plants display rhythmic behaviors as do humans. All these rhythmic phenomena are controlled by biological clocks, internal oscillators that keep time. A physiological cycle with a frequency of about 24 hours is called a circadian rhythm. This clock is set to a period of precisely 24 hours by daily signals from the environment. If an organism is kept in a constant environment, circadian rhythms deviate from a 24 hour period. This supports our idea that day length plays a role in the change of oak trees.
Internet Sources for our Project:
Campbell, Neil A., Jane B. Reece, and Lawrence G. Mitchell. Biology: Fifth Edition. Benjamin/Cummings, an imprint of Addison Wesly Longman, Inc. Menlo Park, CA. 1999.
Lanner, Ronald M. Autumn Leaves: A guide to the fall colors of the northwoods. Northwood Press Inc. Minocqua, WI. 1990.
Lape, Fred. A garden of trees and Shrubs. Cornell U. Press. Ithica, NY. 1965.
Stokes, Donald W. The natural History of Wild Shrubs And Vines. Harper & Row pub. New York, NY. 1981.
Six small honeysuckle bushes
Nine honeysuckle seedlings
Dark Plastic Bag
Clear Plastic Bag
We plan to run two separate experiments to test our two hypotheses. The first experiment will be testing the effects on temperature, and the second experiment will be testing the effects of day length.
A. To test hypothesis A we will test 10 honeysuckle seedlings. Three we will observe in their natural setting as a control group. Seven we will bring inside. To simutate the effects of a frost on leaves we will take a leaf off of one of the saplings as well as leaves from several other native plants and freezing them for different amounts of time (i.e. 1 leaf for one minute, one for 5, one for 10, one for 20, one for 30, and one overnight). All indoor seedlings will be watered three times a week.
We plan to count the number of leaves that have changed color on each seedling outside and inside, and then later to count the number of leaves that remain on the seedling. This will be done once a week.
B. To test the second hypothesis we will use 6 full grown honeysuckle trees. Two will be covered 2 hours before sunset with a black plastic bag to simulate shorter days. Two will be covered with a clear plastic bag at the same time as the black plastic one each day to let light in and adjust for the effects of the bag on the branch. The final two will be uncovered. These will be our control plants.
We plan to count how many leaves are left on each branch once a week.
In class Project:
The class will be split into two groups. Each group, lead by two members of our group, will be asked to survey 10 honeysuckle bushes. 5 on the edge of the forest and 5 in the interior. They will then approximate the percentage of leaves that have changed color on each bush they survey (If at the time that this is done there seem to be few leaves on the bushes then this will change to how many leaves are left on the bushes at the discretion of our group). Both groups will do both areas of the forest so that methodological differences are taken into account. The purpose of this is to see whether the interior bushes or the edge bushes change color faster (or lose leaves faster). The results from this study will then be taken into account in our final report.
We plan to count the number of leaves on the branches. We will make a graph to show the comparison between the different tests we do. So for example if by the end of our testing there is still an abundance of leaves on the branch with the black plastic bag on it, that will prove our hypothesis wrong. We will also record and interpret the color change either through a graph or by using pictures. Also we will count the number of leaves on the seedlings outside and compare that to those inside and to the ones we will perform the cold snaps on. For both of theses tests we will use the t-test and get a p-value and see if there is a significant difference. And use graphs and tables to display our results.
From our observations we obtained the following results:
Plants Location Leaves
A Inside 37 80 69 32
B Inside 27 64 40 13
C Inside 20 12 32 12
D Inside 48 94 82 34
E Inside 15 50 29 14
F Inside 17 88 21 4
G Inside 24 32 58 34
1 Outside 54 0 65 11
2 Outside 72 0 77 5
3 Outside 53 0 88 35
The plants A-G are the 7 plants we kept inside and the plants 1-3 are the 3 plants we had outside. The numbers represent the number of leaves.
With these results we found descriptive statistics, the first table shows these statistics. The mean amount of leaves we started with inside an d outside were 56.1 and the mean amount of leaves at the end were 19.4, so the mean total of leaves lost through out this process was 36.7. Next we performed an unpaired comparison test, these results show the P-value to be .0034.
The first graph compares the amount of leaves lost and their location, inside or outside. This shows the maximum leaves lost inside to be approximately 27 and the maximum leaves lost outside to be approximately 60.
The second graph is a bar graph comparing the amount of leaves gained on each plant. The first three are the plants, which we studied outside, these plants gained no new leaves. In contrast to that, there were many leaves gained inside, where it was warmer and a more controlled environment.
The third graph compares the number of leaves lost on each plant. This bar graph shows that the numbers of leaves lost is greater out side on plants 1-3, than the plants inside A-G.
The last graph is a line graph comparing the leaves started inside vs. outside and the leaves ended inside vs. outside. In this graph one can see the outside plants display a steeper slope than the inside plants.
Sources Of Error:
In our experiment, we took the task upon ourselves to monitor the affects that sunlight and temperature change had on the honeysuckle plants that grew around that area. We had three different experiment sites for these plants.
_ Site #1 was inside of Boyd Science Center, where we had seven potted honeysuckles. The sources of error for this site could have been affected by the consistency in the watering, or the amount of water given to each of the plants. Also the fact that they were placed over a heater.
_ Site #2 was outside of Boyd Science Center, where we had three potted honeysuckles. Even though these plants were located in the outdoors, they were still out of their natural environment because they were potted, rather than firmly planted in the ground. This could have been an important factor in the sources of error for site #2, however this was done to assure that the outside plants got the same sun as the inside plants.
_ Site #3 was located in the small tree line of brush near the tennis courts. When we first attempted our experiment here, we started out with nine honeysuckle plants. Three of them had black garbage bags covering their leaves, and three of them had clear garbage bags covering their leaves. Three plants were left uncovered, but marked, so we would remember which plants we were observing. After monitoring these plants for a few days, we were startled to find that some individual had felt the need to ignore our warning signs and remove the bags from our experiment, causing us to have to start the entire site #3 experiments over again. This time we did the same number of plants again, three black bags, three clear bags, and three without bags. After a few more days of monitoring these plants, we came to discover that our large and numerous warning signs had been trampled into the ground, and our plants had now been chopped from their stalks. In our third and final attempt, we decided to monitor four plants, two with black bags and two with clear. But sadly, we had very little time to run this experiment, and we gathered poor results from our attempt.
In response to our hypothesis the results that we did obtain supported what we thought. The temperature does in some way play a role in the changing and loss of leaves during the fall and winter season. Yet in contrast, due to many sources of error we were unable to get substantial results on whether or not day length played a role in the change of leaves. With our results dealing with temperature difference, we did the unpaired comparison test and found the P-value to be .0034. This is below .05, which is the determining percent of whether or not our observance is based purely on chance alone. Because it is lower than .05, this means there is a significant difference and we reject the null hypothesis and accept that our patterns are based merely on chance alone.
The graphs we have show the significant difference between the plants inside and outside and the amount of leaves lost, between each plant. The second graph that compares the amount of leaves gained with each plant, shows that there were absolutely no plants outside that gained leaves. The conditions inside were environmentally sound enough to produce new buds and leaves. The last graph, point chart, illustrates that there was a greater loss of leaves outside and its slope is much steeper because it is in the cold temperature rather than inside, warm and watered regularly.
In conclusion we do not know what plays a greater role in the change of leaves on honeysuckle. Both temperature and day length could be factors that trees look to as markers of when to take the nutrients from the leaves and detach them from the branches. However our study did get conclusive evidence that temperature plays an important role in leaf change.
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