The climatic factors include rainfall and water, light, temperature, relative humidity, air, and wind. They are abiotic components, including topography and soil, of the environmental factors that influence plant growth and development.
Rainfall is the most common form of precipitation. It is the falling of water in droplets on the surface of the Earth from clouds. Other forms of precipitation are freezing rain, sleet or ice pellets, snowfall, and hail (Eagleman 1985; Miller 2001). The amount and regularity of rainfall vary with location and climate types and affect the dominance of certain types of vegetation as well as crop growth and yield. (Click here to read page devoted to water as a climatic factor).
Light is a climatic factor that is essential in the production of chlorophyll and in photosynthesis, the process by which plants manufacture food in the form of sugar (carbohydrate). Other plant processes that are enhanced or inhibited by this climatic factor include stomatal movement, phototropism, photomorphogenesis, translocation, mineral absorption, and abscission (Devlin 1975; Edmond et al. 1978; Poincelot 1980; Manaker 1981; Abellanosa and Pava 1987).
Light is that visible portion of the solar radiation or electromagnetic spectrum. It is a form of kinetic energy that comes from the sun in tiny particles called quanta or photons, travelling in waves.
Three properties of this climatic factor that affect plant growth and development are light quality, light intensity, and daylength or photoperiod. Light quality refers to the specific wavelengths of light; light intensity is the degree of brightness that a plant receives; and daylength is the duration of the day with respect to the night period.
The degree of hotness or coldness of a substance is called temperature (Eagleman 1985). It is commonly expressed in degree Celsius or centigrade (C) and degree Fahrenheit (F) . This climatic factor influences all plant growth processes such as photosynthesis, respiration, transpiration, breaking of seed dormancy, seed germination, protein synthesis, and translocation. At high temperatures the translocation of photosynthate is faster so that plants tend to mature earlier.
In general, plants survive within a temperature range of 0 to 50 C (Poincelot 1980). The favorable or optimal day and night temperature range for plant growth and maximum yields varies among crop species.
Enzyme activity and the rate of most chemical reactions generally increase with rise in temperature. Up to a certain point, there is doubling of enzymatic reaction with every 10 C temperature increase (Mader 1993). But at excessively high temperatures, denaturation of enzymes and other proteins occur.
Excessively low temperatures can also cause limiting effects on plant growth and development. For example, water absorption is inhibited when the soil temperature is low because water is more viscuous at low temperatures and less mobile, and the protoplasm is less permeable. At temperatures below the freezing point of water, there is change in the form of water from liquid to solid. The expansion of water as it solidifies in living cells causes the rupture of the cell walls (Devlin 1975).
The air is a mixture of gases in the atmosphere. According to Miller (2001), about 75% of this air is found in the troposphere, the innermost layer of the atmosphere which extends about 17 km above sea level at the equator and about 8 km over the poles.
In addition, about 99% of the clean, dry air in the troposphere consists of 78% nitrogen and 21% oxygen. The remainder consists of argon (slightly less than 1%), carbon dioxide (0.036%), and traces of other gases.
The oxygen and carbon dioxide in the air are of particular importance to the physiology of plants. Oxygen is essential in respiration for the production of energy that is utilized in various growth and development processes. Carbon dioxide is a raw material in photosynthesis.
The air also consists of suspended particles of dust and chemical air pollutants such as carbon monoxide (CO), carbon dioxide (CO2), sulfur dioxide (SO2), sulfur trioxide (SO3), nitrogen oxides, methane (CH4), propane, chlorofluorocarbons (CFCs), solid particles of dust, soot, asbestos and lead, ozone and many more.
However, the composition of this climatic factor is susceptible of variation. Recently, there has been a hightenend alarm about the increase of carbon dioxide in the atmosphere.
The amount of water vapor that the air can hold depends on its temperature; warm air has the capacity to hold more water vapor than cold air. According to Eagleman (1985), there is almost one-half reduction in the amount of water vapor that the air can hold for every 10 C drop in temperature.
Relative humidity (RH) is the amount of water vapor in the air, expressed as the proportion (in percent) of the maximum amount of water vapor it can hold at certain temperature. For example, an air having a relative humidity of 60% at 27 C temperature means that every kilogram of the air contains 60% of the maximum amount of water that it can hold at that temperature (Miller 2001).
The amount of water vapor in the air ranges from 0.01% by volume at the frigid poles to 5% in the humid tropics. In relation to each other, high RH means that the air is moist while air with minimal content of moisture is described as dry air. Compared to dry air, moist air has a higher relative humidity with relatively large amounts of water vapor per unit volume of air.
The relative humidity affects the opening and closing of the stomata which regulates loss of water from the plant through transpiration as well as photosynthesis. A substantial understanding of this climatic factor is likewise important in plant propagation. Newly collected plant cuttings and bareroot seedlings are protected against dessication by enclosing them in a sealed plastic bag. The propagation chamber and plastic tent are also commonly used in propagating stem and leaf cuttings to ensure a condition with high relative humidity.
Air movement or wind
is due to the existence of pressure gradient on a global or local
scale caused by differences in heating. On a global scale it consists of
the jet stream flow and movement of large air masses. On the local
scale only a smaller quantity of air moves. Surface winds are lower and
less turbulent at night due to the absence of solar heating (Eagleman
When air that is close to the ground cools, it contracts and the pressure rises; when it warms, it expands and loses pressure. Where both cold and warm air occur in proximity, as over a lake and its adjacent shore, the cold flows to the direction of the warm air or from high to low pressure area to correct the pressure imbalance. This also happens in tropical Asia but in a larger and more complex way, as the monsoon winds (Ripley and The Editors of Time-Life Books 1974).
This climatic factor serves as a vector of pollen from one flower to another thus aiding in the process of pollination. It is therefore essential in the development of fruit and seed from wind-pollinated flowers as in many grasses (click here to read more about pollination).
Moderate winds favor gas exchanges, but strong winds can cause excessive water loss through transpiration as well as lodging or toppling of plants. When transpiration rate exceeds that of water absorption, partial or complete closure of the stomata may ensue which will restrict the diffusion of carbon dioxide into the leaves. As a result, there will be a decrease in the rate of photosynthesis, growth and yield (Edmond et al. 1978).
Each of the above discussed climatic factors has been shown to produce limiting effects on various growth processes. However, the various climatic factors always operate together and interact with each other under natural conditions.
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