In this article we determine the importance of transpiration in plants at three different levels of organization: the plant itself, the ecosystem, and the biosphere, all in terms of entropy production due to transpiration. We propose that transpiration is a thermodynamic imperative rather than a physiological burden for the plant. Plants have not replaced their prevalent metabolism C3 with those of less loss of water, C4 or CAM. We argue that the fact that plants retain higher rates of transpiration along evolution could be explained using thermodynamic criteria.
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