How Scientists are "Tricking" Plants
Colored Mulch Research
Background
Plants are very competitive organisms. They are always competing for space,
nutrients, sunshine, and water. Plants must endure hardships such as disease,
insects, and weather. They must have defense mechanisms and sensory structures
to battle these environmental factors. Plants also have to battle each
other. They have a way to detect each other and a method to compete with
their surrounding neighbors. Plants have a substance called phytochrome
that acts as a sensor to detect changes in the color of light that is reflected
from the surrounding environment. Plants use light as a signal that enables
them to compete with their surroundings. They do not know if the signal
is a neighboring plant, dead plants on the surface of the soil, or even
the color of the soil. The plant recognizes far-red light as the signal.
If the plant detects an abundance of far-red reflection, it thinks that
there must be other plants growing nearby. The phytochrome will then signal
the plant to put more energy (photosynthate) in the top of the plant (shoot)
instead of in the bottom of the plant (roots). The plant, in effect, is
trying to outgrow its competition.
What Is Colored Mulch?
If you have ever picked strawberries, you have seen the black plastic
that covers the soil of each of the rows in a field. Farmers have used
black plastic for years to reduce the amount of weeds near the crop, to
warm the soil in early spring, to keep soil from drying out, and to prevent
the soil from splashing on the fruit. Because this plastic is black in
color, it will absorb the sun's energy and keep more heat underneath the
plastic. Since researchers knew that different colors reflected different
wavelengths of light, they began to ask questions like, "Would other colors
increase plant growth, but provide the same favorable conditions as the
black plastic?" The researchers decided to devise some other colors of
plastic. This plastic with various pigment combinations is called colored
mulch.
What Does Colored Mulch Do?
Colored mulch mimics the reflective patterns of the green leaves of neighboring
plants. The plant will sense the increased ratio of far-red to red light
as though it is reflected from the nearby plants, when in fact it is just
the colored mulch. The colored mulch "tricks" the plant into putting more
energy into shoots to outgrow other plants. Some colored mulch even "tricks"
the plant into producing more and better tasting fruit.
How Did the Scientists Actually "TRICK" the Plants?
Plastic mulch only came in black, white, or clear. In order to make
the other colors, the scientists first used paint to convert the black
plastic to other colors. The scientists then measured the reflection from
colored plastic with an instrument called a spectrophotometer, which records
the amount of light at different wavelengths reflected off the plastic.
The scientists grew tomatoes in soil covered with different colors of mulch
to see what would happen next.
What Were the Results?
Tomatoes that were grown over red plastic had larger shoots and smaller
roots than plants grown over other colored plastic such as white or black.
Since the plastic keeps the soil moist and protected, a slightly smaller
root would not harm the plant. For tomatoes, using the red colored mulch
gave a 20% increase in the first harvest of tomatoes. This is important
to farmers because the first fruit of the season can bring in the most
money. For all crops, the key is the amount of far-red light that is reflected.
In plastic mulch plots, the plant senses an increase of far-red light and
will put more energy into the shoot and less into the root. Therefore,
if the fruit is produced in the shoot, it will usually be larger.
Have Scientists Used Any Other Plants in Their Research?
Scientists have also done research with strawberries, turnips, peppers,
peas, beans, and cotton. They have used colored mulch to determine if other
plants will try to outgrow each other, or put more energy in their shoot.
They found certain colors of reflected light can change the flavor of some
fruits and edible roots (such as turnips and carrots).
Why Is this Research Important?
When colored mulch is used in agriculture, crops are expected to produce
larger fruit and possibly even better tasting fruit. This could mean larger
and better tasting fruits and vegetables in grocery stores or in home gardens.
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