Draft 1 How temperature and daylength effect seasonal change of Oak trees

This topic submitted by Megen Leigh, Nikki Mihevic, Erica Govich, and Dan Kehn at 4:55 pm on 10/5/01. Additions were last made on Friday, April 19, 2002. Section: Myers

Abstract:

Our lab group has decided to discover what factors determine the rate of change in the color and losing of oak 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 branches on several trees 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.

Thesis:

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. Cold snaps will accelerate the rate that the leaves change color and fall. Warmer temperature will reduce the rate this change occurs.

Introduction:

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 leafÕs 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 treeÕs 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 treeÕs 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:
v www.na.fs.fed.us/spfo/pubs/misc/leaves/leaves.html
v www.na.fs.fed.us/spfo/pubs/misc/autumn/autumn_colors.html
v www.dnr.state.wi.us/org/caer/ce/eek/veg/trees/treestruecolor.htm
v www.treehelp.com/features/features-fall-colors-1.html
v http://www.accuweather.com/iwxpage/paws/fallfaq.htm
v http://www.esf.edu/pubprog/brochure/leaves/leaves.htm
v http://www.ces.ncsu.edu/nreos/forest/topics/leafco~1.html
v www.sciam.com/askexpert/environment18.html
v www.nps.gov/blri/flowers.htm
v www.enn.com/enn-newsarchive/1999/09/090299/drfoilage_5414.asp

Book Sources:
Campbell, Neil A., Jane B. Reece, and Lawrenve G. Mitchell. Biology: Fifth Edition. Benjamin/Cummings, an imprint of Addison Wesly Longman, Inc. Menlo Park, CA. 1999.

Materials:

Six Oak Trees
Nine Oak Tree Seedlings
Camera
Dark Plastic Bag
Clear Plastic Bag
Refrigerator/Freezer

Methods:

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 9 oak seedlings. Three we will observe in their natural setting as a control group. Six we will bring inside. Three of those six will be kept in the artificially warm environment at all times while the others will be given "cold snaps" once a week at night to make sure that they get enough sunlight. In order to assure that we donÕt kill the saplings we will test for safe freezing/refrigerating times by taking a leaf off of one of the saplings and freezing it for different amounts of time (i.e. 1 leaf for one minute, one for two, one for three, etc.). 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 oak trees. We will use 3 different branches on each tree of approximately the same size to run the experiment. One of these three will be covered 2 hours before sunset with a black plastic bag to simulate shorter days. One branch will be covered with a clear plastic bag to let light in and adjust for the effects of the bag on the branch. The final branch will be uncovered. This will be our control branch.
We plan to count the number of leaves that have changed color on each branch and then how many leaves are left on each branch once a week.

Results:

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.

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