The major mechanism of reducing heat from the crop canopy is:
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Monitoring canopy temperature using infrared thermometers is a standard way to assess crop water stress.
A high canopy temperature relative to the ambient air indicates stomatal closure and water deficit (reduced transpiration).
Step 1: Understanding the Concept:
Crop canopy temperature is determined by the balance of incoming solar radiation and the processes that dissipate this thermal energy.
Plants regulate their internal and canopy temperatures through physical and physiological heat dissipation mechanisms. Step 2: Detailed Explanation:
Transpiration is the physiological loss of water vapor from plant leaves through the stomatal openings.
This phase change of water from liquid to vapor requires energy, known as the latent heat of vaporization.
As water evaporates from the stomatal cavity, it absorbs approximately 540 calories of heat per gram of water evaporated, directly cooling the leaf tissue and the surrounding canopy.
This evaporative cooling is the most effective physiological mechanism plants use to prevent thermal stress under intense solar radiation.
Let us compare this with the other options:
1.Advective heat losses (A): This refers to the lateral transfer of heat by wind, which can cool or warm the canopy depending on the temperature of the air mass, but it is not a plant-controlled mechanism.
2.Evaporation (B): This is the purely physical loss of water from the soil surface, which cools the soil but does not directly regulate the leaf canopy temperature.
3.Heat absorption by soil (D): The soil absorbs heat, which actually raises the ambient temperature of the canopy through sensible heat flux rather than cooling it. Step 2: Final Answer:
The major physiological mechanism used to dissipate heat from the crop canopy is Transpiration.
