10 Integrated2-21

10 Integrated2-21 - Integrated plant responses to water and...

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Integrated plant responses to water and heat stress
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High temperatures are not the only potentially harmful  environmental conditions to which organisms living in the desert are  exposed. For example, solar radiation levels may be very high, atmospheric  humidities may be very low, and wind speeds may fluctuate  markedly. In order to survive in the desert, organisms must be able to function  efficiently under this entire set of environmental conditions.
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It thus becomes important to examine the interaction between the  various environmental conditions. In other words, we can ask the question: what is the combined effect  of these various conditions on organisms living in the desert?
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In order to answer this question, we need to develop a quantitative  relationship that describes the influence of these environmental  conditions on the energy balance of an organism. The starting point for this analysis is the principle of conservation of  energy, also known as the first law of thermodynamics.
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The principle states that energy can be neither created nor destroyed,  but only changed from one form to another.  With respect to the surface of an organism, such as the surface of a  leaf, this principle implies that: energy in = energy out + energy stored
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We may expand this equation by considering the various forms of  energy exchange between leaves and their surroundings: absorbed shortwave radiation + absorbed longwave radiation =  emitted longwave radiation + convection + evaporation + storage
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absorbed shortwave radiation  +  absorbed longwave radiation  =   emitted longwave radiation  + convection + evaporation + storage
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*Some key points about the radiation terms: All physical bodies with temperatures above absolute zero emit  electromagnetic radiation The wavelength of maximal emission is inversely related to the  temperature of the body 
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*For example, the wavelenth of maximal emission -for the sun, with an effective surface temperature of about 6000  K, is about 0.5 
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