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2) Decreased relative humidity outside the leaf will increase the water potential gradient. Relative humidity: Drier surroundings give a steeper water potential gradient, and so increase the rate of transpiration. Wind: In still air, water lost due to transpiration can accumulate in the form of vapor close to the leaf surface.
At lowered light levels the leaves fold down; timelapse recorded at ~750x actual speed and covering a 1.5 hr period of time. In biology , nastic movements are non-directional responses to stimuli (e.g. temperature , humidity , light irradiance ) that occur more rapidly than tropisms and are usually associated with plants .
Transpiration is a larger component of evapotranspiration (relative to evaporation) in vegetation-abundant areas. [14] As a result, denser vegetation, like forests, may increase evapotranspiration and reduce water yield. Two exceptions to this are cloud forests and rainforests. In cloud forests, trees collect the liquid water in fog or low ...
Stomatal conductance, usually measured in mmol m −2 s −1 by a porometer, estimates the rate of gas exchange (i.e., carbon dioxide uptake) and transpiration (i.e., water loss as water vapor) through the leaf stomata as determined by the degree of stomatal aperture (and therefore the physical resistances to the movement of gases between the air and the interior of the leaf).
Humidity affects the energy budget and thereby influences temperatures in two major ways. First, water vapor in the atmosphere contains "latent" energy. During transpiration or evaporation, this latent heat is removed from surface liquid, cooling the Earth's surface. This is the biggest non-radiative cooling effect at the surface.
For example, laundry on a clothes line will dry (by evaporation) more rapidly on a windy day than on a still day. Three key parts to evaporation are heat, atmospheric pressure (determines the percent humidity), and air movement. On a molecular level, there is no strict boundary between the liquid state and the vapor state.
Transpiration from plants is another typical source of water vapor. [25] Lastly, cool or dry air moving over warmer water will become more humid. As with daytime heating, the addition of moisture to the air increases its heat content and instability and helps set into motion those processes that lead to the formation of cloud or fog. [26]
Osmotic absorption becomes more important during times of low water transpiration caused by lower temperatures (for example at night) or high humidity, and the reverse occurs under high temperature or low humidity. It is these processes that cause guttation and wilting, respectively. [66] [67] Root extension is vital for plant survival.