2. Soil-Plant-Atmosphere System

Water can evaporate from all wet surfaces if there is a flux of energy. The most important process for biomass production and proper functioning of the biosphere is evapotranspiration. Evapotranspiration is, however, the process of water transport through the soil-plant-atmosphere system (SPAS). Every subsystem of the SPAS can strongly influence the evapotranspiration process. This chapter contains basic information about all three subsystems of the SPAS. Basic properties of water (water vapor), soil, plant (canopy), and atmosphere are presented and their role in the evapotranspiration process is discussed. It is shown that soil water is not pure water but a solute, and salinization during evapotranspiration can occur. The role of carbon dioxide and its increase in the SPAS is discussed, mainly the possible effect of carbon dioxide on the greenhouse effect.