Energy, Plants, and Ecology

The environmental factors affecting the flow of energy between a plant and its environment are described. These factors are solar and thermal radiation, air temperature, water vapor density of the air, and wind speed. The mechanisms of radiation, convection, and transpiration which transfer energy between the plant and the environment are expressed in analytical form. An example is given of a 24—hour cycle for a plant illustrating the daily variation of each of these factors and of the resulting plant temperature. Basic plant properties, such as absorptance to radiation, convection coefficient, and water vapor diffusion resistance, determine the extent to which the environment influences the energy content and temperature of the plant. Photosynthesis is light and temperature dependent, and other physiological processes are temperature dependent only. Maxima and minima in photosynthetic activity occur during a day as a consequence of changes in light intensity and leaf temperature produced by varying environmental conditions. The ecological significance of these environmentally influenced physiological processes is enormous in terms of productivity and competition.