The Fall
Colors
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Do you
know why leaves change their colors during Fall ? |
Most of
the nutrients responsible for the tree's growth are produced
in the leaves, in various cells containing chlorophyll. This
chemical is what gives plants their green color and is responsible
for the photosynthesis.
The photosynthesis
is the process in which the chlorophyll absorbs from sunlight
the energy necessary to transform water and a gas called carbon
dioxide into carbohydrates (glucose and starch), which are used
for the plant as nourishment.
 During Summer, the leaves prepare for the
Fall making more glucose than necessary, turning all excess into
starch which is stored for the future. Small tubes which pass
through special layers of cells located at the base of each leaf,
called separation layers or abscission, carry water to the leaf
and the food produced from it back to the tree.
During
Fall, these cells become larger, reducing and then cutting off
the flow between the leaves and the tree, trapping glucose and
waste products in the leaf. As there isn't enough light or water
for photosynthesis to renew it, chlorophyll begins to disappear.
 The chlorophyll present
in the leaves during Summer and Spring, masks the other colors
that are also present in the leaves but which appear only during
Fall. When the chlorophyll begins to disappear, the other colors,
such the yellow and orange from carotenes and xanthophyll pigments,
which give the orange color to a carrot and the yellow color
to a banana, become visible.
 The red and purple
colors from anthocyanin pigments, which are common in purple
grapes, red apples and violets are formed in the dying leaves
during Fall. The glucose that was trapped in the leaves gives
them the red color and the waste products are responsible for
the brown color.
 The colors the leaf
will show depends on the amount of each pigment that are present
in the leaf. Temperature, light and water are also the environmental
factors that influence the degree and the duration of the colors.
After the
abscission swells and the leaves stop the food production, they
will then be sustained only by a few strands which will make
them fall on the ground when they break.
The process
of loosing leaves is important to renew those that are damaged,
destroyed by insects or weather, and to provide nourishment for
the plants. When the leaves fall, they become food for bacteria
and fungi which break them down into substances that will be
absorbed by plant roots. |
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