The shedding of leaves in dry or cold season by deciduous plants is a xeromorphic adaptation. Loss of water is more from the leaves that have more stomata on the lower surface than those having equal number on both the surfaces. This environmental factor affects transpiration by regulating stomatal movement and atmospheric demand. As temperature increases, the water holding capacity of that air increases sharply. So the photosynthesizing leaf loses substantial amount of water by evaporation. These include thick cuticles, thick cell walls, sunken stomata, and hairs or pubescence.
Our mission is to provide an online platform to help students to share notes in Biology. The rate of transpiration depends upon the saturation deficit. Light affects the rate of transpiration in two ways. When stomata are open, transpiration rates increase; when they are closed, transpiration rates decrease. Transpiration has side effects for other organisms in an ecosystem. This creates a traspiration stream, pulling water up from the root. External or Environmental factors : 1.
Small leaves or leaflets can dissipate heat by convection better than large leaves, thus maintaining the leaf at ambient temperature instead of above air temperature from solar absorption. The relatfte humidity decreases or increases with every rise in the temperature. Factors affecting the Transpiration Rate The list below gives the factors which affect the transpiration rate. Stomatal frequency varies with different species. One variety Pride of Saline Corn had greater leaf area of 14,568 sq.
Plants have a limited ability to regulate their movement of water, but environmental factors nonetheless have significant effects on transpiration. The wind removes the air of that area and is replaced by fresh air and results in the increase in the rate of transpiration. Stomata has two guard cells which are responsible for their opening and closing. According to Devlin 1975 , the surfaces of leaves of different plant species may contain from 1,000 to 60,000 stomata per square centimeter. Therefore, the rate of transpiration is high during the daytime and at night, only some amount of water is lost by cuticular and lenticular transpiration. A corn plant loses 3-4 litres of water per day, whereas a tree-sized desert cactus with no foliage loses less than 25 ml of water per day. At these temperatures the stomatal apertures or opening are generally widest.
At low humidity there is a lower concentration of water molecules in the air around the leaves. Firstly, light causes stomata to open. Temperature An increase in the air temperature warms the water inside the leaves more quickly causing it to evaporate quicker. The rate of transpiration increases with the increase in the availability of water in the soil. Water in the leaf cells forms a thin layer on their surface. Atmospheric Humidity: The rate of transpiration is roughly inversely proportional to atmospheric humidity.
High humidity means the air around the leaves is already saturated and has a higher concentration of water molecules than inside the leaves. Likewise, the presence of dry epidermal hairs or pubescence on the leaf surfaces tends to lessen the rate of transpiration by acting as wind breaks. The mode of action of light is both direct and indirect. Practical application: It is common to trim the leaves of broadleaved seedlings before transplanting, like coffee, to one-third or thereabout of original length to reduce transpirational loss. The number, size, position, and degree of opening control most transpiration. Several structural features lessen the rate of transpiration.
Leaves that develop in open sun also have thicker cuticles than those which develop under shade. Rise in temperature increases the rate of water evaporation from the cell surface which opens the stomata and decreases the relative humidity of the atmosphere. As a result, there is rapid diffusion of water vapour from humid atmosphere inside the leaf to outer dry atmosphere. Boundary layer — The boundary layer is a thin layer of still air hugging the surface of the leaf. But the leaves constitute major portion of stomata. It also cause the stomata to open, thus more transpiration occurs during the day and the rate is higher on a sunny day compared to a cold dull day. Temperature as an environmental factor affecting transpiration also relates to water potential and relative humidity.
It helps maintain a certain moisture level in an environment, depending on the number and types of plants in an environment. As water is transpired or otherwise used by the plant, it is replaced from the reservoir on the right. Consquently, the rate of transpiration is increased in bright sunlight. In addition, there are fleshy or relatively thick leaves, stems and fruits which, upon exposure to sunlight, results to internal temperatures which exceed that of sorrounding air. In the atmosphere, the water forms clouds, and then it falls back to earth again as rain or snow. Also, plants can use transpiration as a method of cooling themselves. These special cells help to regulate the rate of transpiration by opening and closing the stomata A number of external factors that affect the rate of transpiration, namely: temperature, light intensity, humidity, and wind.
The amount of water lost this way is very small compared to stomatal transpiration, but as with cuticular transpiration, it may increase if a plant is in a dry environment. Light Plants transpire more rapidly in the light than in the dark. The amount of water does not change, just the ability of that air to hold water. The rate at which transpiration occurs refers to the amount of water lost by plants over a given time period. Plants cannot continue to transpire without wilting if the soil is very dry because the water in the xylem that moves out through the leaves is not being replaced by the soil water. So it has an indirect influence on the rate of transpiration. Leaves may also change shape to maintain a boundary layer, such as the curling or rolling of grass blades during drought.