Effect of Plant Environment
Temperature
There are three
important temperatures for plants: a minimum temperature at which the plant
will stop growing and injury will occur; a maximum temperature above which a
plant will stop growing and permanent injury will occur; an optimum temperature
somewhere between these two,where the plant grows best. In the range between
minimum and optimum, the plant will grow faster as the temperature.
Nutrients
Sixteen elements
are necessary for most plants to grownormally. Ten elements are used in relatively
large amounts,and they are called major elements or macro nutrients. These
major elements are carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium,
calcium, magnesium, sulfur, andiron.The other six elements are used by plants
in small amounts and are called trace elements, minor elements, or micronutrients.
Even though these minor elements are needed in small amounts, they are essential
to normal plantgrowth. These micro nutrients are boron, copper, zinc,
manganese, chlorine, and molybdenum. A fertilizer is any material, either
organic or chemical, that provides one or more ofthese 16 essential elements.
Plant nutrients that most often need replacing in the soilare nitrogen,
phosphorus, and potassium. Fertilizers that contain all three are called complete
fertilizers. Nitrogen and potassium are soluble in water and are easily carried
away by heavy watering or rainfall.Phosphorus is not very soluble in water and
needs to be added to the soil less often. Unlike other nutrients that move dissolved
in water to the root, phosphorus is usually takenup by the root's growing to
where the phosphorus is.The ability of the plant to take up nutrients from the
soiland use them for its growth depends partly on the pH of thesoil. Soil pH
refers to the acidity or alkalinity of the soil. A14-point scale is used to
measure pH. Seven is neutral;below 7 is acid, and above 7 is alkaline
(basic).An acid soil is sometimes called a sour soil; basic soil issometimes
called a sweet soil. Plants usually prefer a slightly acid soil with a pH near
6.5. At a pH of 6.5, all elementscan be taken up by the plant if they are
present in the soil. Ifthe pH goes up too high or down too low, some of the
essentialelements will be less available to the plant.You can increase the pH of
an acid soil by adding limestone or dolomite (lime stone that contains
magnesium). If asoil pH is too high (alkaline), it can be lowered by adding anacid
forming material such as sulfur to the soil.Some plants die if the temperature
around them drops by low freezing. Plants that cannot live in freezing temperatures
are often called tender plants. Some plants are so ten der they can be injured
by temperatures above freezing. This is called chilling injury, and it results
from abnormal processes occurring in the plant. Cucumbers can suffer from
chilling injury. The plants look water soaked from inside. Then they turn black
and die. As long as ice does not form within the plant, freezing injury will
not occur. Other structures used in horticulture that have the same general
features as a greenhouse but are smaller are hotbeds, coldframes, cloches, and
hot caps. Another way to modify temperature is with the use of mulch. A mulch
is any material used to cover the surface of the soil. Black or clear plastic
materials are used in spring to warm up the soil and permit early planting.
Mulches in winter are used to keep the soil cold.
Light
The green plant
is a solar (sun) collector transfer ring light energy into energy foods
(sugars) for the plant. Plants respond to light intensity (bright ness), quality
(color), and duration (photoperiod or day length). Light intensity or bright
ness affects the amount of photo synthesis that occurs. When light intensity is
lowered, photo synthesis is reduced. Some plants will grow in areas of lowlight,
such as the floor of a jungle. This is why tropical foliage plants grow so well
indoors. Grasses that are native to the plains generally require high light
intensity. Sudden exposures of plants to high light intensity can cause leaf
scorch or sun burning with symptoms of large brown, dead areas. High light
intensity can also cause fading of flower color. Light quality refers to the color
of white light or to a part of the whole range of light. White light is made up
of all the colors in the rainbow. Chlorophyll, which gives the plant its green
color, absorbs light in the blue violet and orange-red portion and uses it in
pho to synthesis. Ultra violet light is important in the coloration of some
fruits and the development of autumn color in leaves. The duration of light
each day (photoperiod or day length) is important in the development of some
plantsin short days.
Water
Water is important
for normal plant growth. Water provides the plant's rigid structure. Water
moving into the plantcauses it to expand and grow. Water evaporating from the leaf
cools the leaf. Water dissolves nutrients from the soil so they can be
transferred to the plant, and water is also necessary for photosynthesis. Lack
of water can cause serious problems. The plant will lose its rigid structure
and wilt. Because water is no longer moving into the plant, the plant cannot
grow. The plant cannot cool itself and may increase in temperature to dangerouslevels.
The plant cannot take up the nutrients it needs without water. Plants that grow
in areas where there is little water have special structures to help the plants
save water. Plants can be given too much water. Sudden flooding of the soil can
cause the roots to die because water fills the air spaces, cutting off the
oxygen supply to the roots. Roots cannot live long without oxygen. The amount
of water a plant needs depends on light, temperature, and the humidity of the
air around the plant. The higher the temperature and the greater the light
intensity, the greater will be the plant's need for water.
Air
Four main parts
of air are important to the plant: carbondioxide, oxygen, nitrogen, and water.
Carbon dioxide
occurs in very small amounts in the air, but it is essential for
photosynthesis.Oxygen is needed by all the parts of the plant, but the root
system is most likely to suffer from an oxygen short age. A good soil will have
50 percent pore space. This pore space can contain either air or water. When
the space contains about half air and half water, there is a good balance, but
when all the pore space becomes filled with water, as when you overwater a
houseplant or when there is a drenching rain, the soil becomes saturated and
there is not enough oxygen for the plant roots. If the soil stays too wet for
several days, it can cause root death, and then diseases and rots will set in
more easily. Nitrogen is important for some plants. Nitrogen fixing bacteria
live on the roots of certain plants. These bacteria take up nitrogen from the
air, and the plant does not need to be given nitrogen in fertilizer. Water in
the air is important because if affects the amount of water the plant will lose
in transpiration. Air does not usually hold as much water as it could (less
than 100 percent relative humidity). This means it acts like a drying agent,
constantly removing water from plants.
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