Factors Affecting Transpiration
Transpiration roses are influenced by internal and external factors. Internal
factors that affect transpiration include leaf morphology and anatomy, including
stomata. Meanwhile, external factors that affect transpiration are sunlight,
temperature, air humidity, wind, and water conditions in the soil (Pujiwati, 2018).
1. Internal factors that affect transpiration
a. Leaf morphology
Leaf morphology that affects transpiration includes leaf area, leaf
thickness, and leaf surface. The wider and thinner a leaf is, the more
transpiration increases. On the other hand, transpiration can decrease
due to the presence of trichomes (fine hairs on the leaves).
b. Leaf anatomy
The presence of a waxy layer on the surface of the leaf affects
transpiration. The waxy coating on the surface of the leaf can inhibit
transpiration. Thus, leaves whose surface has a transpiration wax layer
are low.
c. Stomata
Transpiration is affected by stomata, including their number, shape,
location, and distribution. The more stomata there are, the more
transpiration increases. The oval shape of the stomata hole affects the
intensity of the water that comes out during transpiration. Stomata holes
that are close together can decrease transpiration because the exit of
water from a hole can inhibit the exit of water from adjacent holes. In
addition, stomata on the axial part (lower surface) of the leaf can reduce
the occurrence of transpiration.
2. External factors that affect transpiration'
a. Sunlight
Sunlight spurred the opening of the stomata. In a state of little or no
light, the stomata will close.
b. Temperature
The higher the temperature, the faster the transpiration will be. The
effect of temperature on leaf transpiration can also be viewed from
another angle, namely in relation to the pressure of water vapor inside
the leaf and outside the leaf. The increase in temperature is able to
increase the vapor pressure inside the leaves.
c. Air humidity
If the humidity of the air in the atmosphere is higher than the humidity
of the leaves, then the rate of transpiration is getting lower.
d. Wind
The stronger the wind blows, the higher the rate of transpiration.
e. Water conditions in the ground
Stomata Mechanics and Stomata Control Mechanism
The mechanics of the stomata is the mechanism for opening and closing
the stomata. Stomata comes from the Greek word stoma which means hole or
porous. Stomata are small, oval-shaped holes surrounded by two specialized
epidermal cells called guard cells. The covering cell is in the form of epidermal
cells that have undergone changes in shape and function that can regulate the size
of the holes they flank
In some plants, there are two or more cells adjacent to the cover cell that are
morphologically and functionally different from other epidermal cells and can be
combined called neighboring cells. Closing cells include living cells and contain
chloroplasts that function to regulate the opening and closing of the stomata.
1. Stomata Opening Mechanism
The opening of the stomata is induced by the accumulation of
potassium ions (K+) in the guard cells. Potassium ions are solutes, while
the solvent is water. The high or low potential of water is influenced by the
amount of solute in the cell's fluid. The more material is dissolved, the
lower the cell's osmotic potential will be. In a state of constant turgor
pressure of the cell, the water potential will decrease. If the amount of
solute increases, which in this case is potassium ions, it spurs water to enter
the guard cell. The ingress of water into the guard cells causes the turgor
pressure on the guard cells to increase. If the turgor pressure of the two
guard cells increases, then the stomata will open.
The entry of potassium ions in guard cells is stimulated by the
presence of light. The light that is more effective at stimulating the entry
of potassium ions is blue light. In addition to playing a role in regulating
the entry of potassium ions into guard cells, blue light also plays a role in
the breakdown of starch molecules to produce phosphoenol pyruvate (PEP)
which can receive CO2 for the formation of malic acid.
Potassium is a cation (a positively charged ion). In order for the
neutrality of the electrical charge in the cell to be maintained, it must be
balanced with anions (negatively charged ions). In some species, the anion
is chlorine (Cl-). Thus, in order for the electrical charge in the cell to remain
neutral, the entry of K+ ions is accompanied by the entry of Cl- ions.
However, in some studies it has been reported that the entry of K+ ions
without the inclusion of Cl- ions. In this situation, hydrogen ions (H+) exit
the guard cell so that the neutrality of the electrical charge is maintained.
The hydrogen ions present in the guard cell come from organic acids
synthesized by the guard cell in response to factors that induce the opening
of the stomata.
2. Stomata Closure Mechanism
The closure of the stomata is induced by the accumulation of the
hormone absicic acid (ABA). The presence of very low concentrations of
ascetic acid can spur stomata closure. The ascytic acid in leaves is located
in three cells, namely the cytosol, chloroplast, and cell wall. Abscisic acid
is synthesized in the cytosol and then accumulated in chloroplasts. In
addition to the cytosol, ABA is also in the leaf mesophyll cells. The
mechanism of opening and closing stomata (stomata conductivity) is
influenced by several factors, including light intensity, air humidity, wind
speed, moisture content, and soil moisture
