Leaf pubescence as a possibility to increase water use efficiency by promoting condensation

There is various evidence that the presence of condensed water, e.g. dew, improves plant water relations. Because particularly plants in drier environments are expected to benefit from atmospheric water, it may be assumed that special adaptations promoting exploitation of dew water evolved in these habitats. Surface characteristics affect dewfall and retention of dew water. Leaf surface characteristics such as hairs (trichomes), which are often present in plants of arid environments, may therefore play a substantial role in dew harvesting. In this study, it is analysed to what extent (1) the presence of hygrophilic aerosoles promotes dewfall by reducing vapour saturation pressure (early condensation'), (2) dew water can be stored within a dense trichome layer, (3) the presence of dew water increases humidity directly above the leaf surface, thereby reducing water loss from the leaf interior by decreasing the water potential gradient between leaf interior and exterior, and (4) dew evaporation reduces transpiration further by evaporative cooling. A physical framework is provided in this contribution that shows that these processes are in fact possible under natural conditions. Copyright (c) 2014 John Wiley & Sons, Ltd.