Factors of environment affecting the rate of transpiration
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Step-by-step explanation:Enumerated below are the environmental factors affecting transpiration in plants. These factors are described as "environmental" to distinguish them from those genetic factors which are inherent in the plants. They are also described as external factors, that is, outside of or external to plants. Specifically they are climatic factors, that is, they are elements of the climate.
These factors are the same climatic factors which can either promote or inhibit plant growth and development and, eventually, crop productivity.
is important in crop agriculture to be able to familiarize with these environmental factors affecting transpiration in order to be guided on the proper timing of farm activities. Likewise, it should be essential in devising strategies to reduce evapo-transpirational water loss or otherwise balance transpiration rates with water absorption and dry matter production. The ultimate objective is to achieve a net surplus of biomass, that is, increased crop production.
Thus, for example, transplanting late in the afternoon and providing artificial shade to newly transplanted seedlings in open sun are sound practices to improve plant survival. A stable and abundant water supply is necessary to maximize production in crops grown under conditions that favor rapid evaporation. Otherwise, a strategy has to be effected, like using plastic mulches, to minimize excessive water loss from the soil without curtailing plant exposure to sun.In general, plants transpire fastest under the following climatic conditions: (a) bright day, (b) dry air, (c) moist soil, (d) warm temperature, and (e) windy day.
The various environmental factors affecting transpiration, particularly the rate of transpiration, are briefly discussed below. They operate in influencing transpiration, however, interconnectedly.Light. Light, specifically light intensity, is probably the most obvious among the environmental factors affecting transpiration in plants. It has a controlling effect on the opening of the stoma through which water primarily escapes in gaseous state. In general, transpiration rate is high during daytime, particularly when light is bright, than during night time.
The stomata are typically open during daytime, allowing the entry of CO2 and the exit of O2. The opening of the stomata likewise enables the escape of water as water vapor in the process of stomatal transpiration. Except in CAM plants, the stomata are close at darkness between sunset to sunrise. Relative Humidity. This environmental factor affects transpiration by regulating stomatal movement and atmospheric demand. At high RH (moist air), the stoma tends to close and thus limit the exit of water vapor from the plant. Further, high RH means that the water-potential gradient (also water vapor concentration and vapor pressure gradient) from plant to the atmosphere will be minimal compared to when RH is low. In addition, at high RH the atmosphere contains more water and has low atmospheric demand, meaning that it has limited capacity to absorb more water.At 50% relative humidity at a temperature of 20°C, water potential Ψw of the atmospher is -93.5 MPa but at 90% RH, water potential will be -14.2 MPa. On the other hand, the typical water potential of the leaves of a small tree that grows with sufficient soil moisture will be -1.5MPa (Moore et al. 2003). In both RH, transpiration occurs whereby water vapor moves outward from higher to lower water potential or from less negative to more negative water potential values, i.e., from Ψw= -1.5MPa to Ψw= -93.5 MPa (at 50% RH) and from Ψw= -1.5MPa to Ψw= -14.2 MPa (at 90% RH).Transpiration rate will be faster at 50% than at 90% RH. At 50% RH, the water potential gradient is more steeper (93.5 MPa – 1.5 MPa = 92 MPa) compared to 90% RH (14.2 MPa - 1.5 MPa = 12.7 MPa). Low RH also favors faster transpiration due to stronger atmospheric demand.
But as long as the stomata are open, transpiration occurs, even at saturated condition of 100% RH. In this case the expelled water vapor readily