External Factor Influencing Growth and Development Of Plants
Minggu, 22 November 2020
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External Factor Influencing Growth and Development Of Plants
External or environmental factors are the influences of climate, soil, and biota of the plant’s habitat. All of these affect the growth and development of plants, together with all of internal factors as well. The following explains how each external factor influences plant growth and development. '
Temperature
Temperature affects the processes of plant photosynthesis, respiration, and transpiration. High temperatures influences water content of plant tissues. The plant strategys to overcome high temperatures is by increasing the rate of transpiration (loss of water through leaves). Temperature also influences enzymatic activities in plant metabolism.
Every plant needs a different range of temperatures for its optimal growth and development. Generally, plants can live in temperatures ranging from 0°C to 45°C. However, the optimal temperature is usually 20-25°C. The optimum temperature for corn plants (Zea mays), for instance, is 30 to 35°C. Corn plants cannot grow below 12°C.
Important Concept
- Auxin plays role in stimulating cell elongation process.
- Gibberellin helps stimulating embryonic development and growth.
- Ethylene functions in fruit ripening and leaf shedding.
- Cytokinins play role In cell division (cytokinesis).
- Abscicic acid functions in aging process and leaf shedding.
- Brassinosteroid plays a role in plant resistancy to stress condition.
- Traumatic acid plays role in cell regeneration when the plant experiences tissue damage.
The optimum temperatures for growth of plants relates to their original habitat. Tropical plants need a relatively higher temperature to grow compared to sub-tropical or polar plants.
Sunlight
Sunlight very much affects photosynthetic plants (usually green) because it is needed for photosynthesis. Photosynthesis is the basic plant process that produces food. This food determines the availability of energy by which plants grow and develop.
Sunlight also influences growth. Plants kept in the dark grow much faster. However, they are pale, thin, and their leaves may not develop well (undergo etiolation). This occurs because of a lack of light, therefore the auxin is at its maximum function to elongate plant cells. On the contrary, plants in bright light intensity grow slower. They are relatively shorter, develop good leaves, and are green in color. This is because of the inhibition of auxin is influenced by the presence of sunlight.
(a) Peanut plant that grows in the dark experiences etiolation
(b) peanut plant growing in normal light does not.
Plant responses toward the period of sunlight exposure is termed photoperiodism. In subtropical countries that undergo four seasons, sunlight exposure varies each season. Based on these responses, plants are grouped into short-day plants, long-day plants, and neutral-day plants.
FIGURE 1.13 (a) Short-day plant, such as aster, (b) Longday plant, such as spinach, (0) Neutra|-day plant, such as sunflower.
(b) Longday plant, such as spinach,
(c) Neutra|-day plant, such as sunflower.
Short-day plants
Short-day plants produce flowers when the light exposure period (day time) is shorter than the darkness period (night time). These plants produce flowers at the end of summer or autumn, such as aster, Chrysanthemum, and dahlia. Long-day plants
Long day plants produce flowers when the daylight period is longer than the night period. They bloom during spring, such as spinaches, potatoes, and wheat.
Neutral-day plants
Neutral day plants are not influenced by the period of sunlight exposure, such as sunflowers, roses, and cotton.
Plant responses toward sunlight exposure include the processes of dormancy, germination, stem and root development, and flowering. Phytochrome pigment is responsible for controlling this plant’s response.
In the same plant, leaves that function in photosynthesis receive different exposure to light intensity. This creates differences in leaf structure.
Leaves that receive more sunlight photosynthesize at a faster rate. The effect is palisade parenchymal cells are structured in more than one layer. To reduce transpiration, the cuticle thickens. However, plants exposed to less sunlight contain more waters and more mesophyll cells.
Important Concept
Phytochrome is a pale-blue protein distributed all over plant tissues. Low concentrated phytochrome in plants is able to receive red wavelength (A = 660 nm) and infrared wavelength (A = 730 nm).
Water, pH, and oxygen
Water Is a very important compound in maintaining turgor pressure of cell walls. Some other functions in plants are:
- to determine photosynthetic rate;
- a universal solvent during plant growth and development;
- to transport soil nutrients;
- to distribute photosynthesis products to all parts of the plant;
- as a medium for cellular chemical reactions (metabolism).
Soil pH influences plant growth and development. Soil pH is determined by the soil types. For example, red-yellow podzolic soil is very acidic and is not ideal for plant growth. Its low pH needs to be increased by adding limestone to the soil for example. Extreme soil pH may be toxic to most plants.
Oxygen is a limiting factor for all organisms. This condition also applies to plant growth and development. Oxygen concentration is determined by the medium where the plant is present. The roots of plants need good aeration conditions to obtain oxygen. Therefore, farmers always plough their field regularly. Good aeration can increase root respiration and also better distribute minerals and nutrients from the soil to all parts of the plant.
Nutrients
Plants need nutrients for their survival. Nutrients needed in major amounts am called macronutrients. Macronutrients are carbon, oxygen, hydrogen, nitrogen, sulfur, potassium, calcium, phosphor, and magnesium. Nutrients needed in small amounts are micronutrients, such as chlorine, iron, boron, manganese, zinc, copper, and molybdenum.
Lack of nutrients both in the soil and the plant’s media may cause a deficiency. Nutrient deficiencies cause imperfect growth and development.
Functions of macronutrients and their deficiencies are listed in Table 1.1. Function Of Macronutrient and Their Deficiencies
Important Concept
External factors that influence plant growth and development are temperature. sunlight. water. pH, oxygen. and nutrients.
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