Wetting mechanism and morphological adaptation; leaf rolling enhancing atmospheric water acquisition in wheat crop-a review

Abstract

Several plant species such as grasses are dominant in many habitats including arid and semi-arid areas. These species survive in these regions by developing exclusive structures, which helps in the collection of atmospheric water. Before the collected water evaporates, these structures have unique canopy structure for water transportation that plays an equivalent share in the fog-harvesting mechanism. In this review, the atmospheric gaseous water harvesting mechanisms and their affinity of measurements were discussed. Morphological adaptations and their role in the capturing of atmospheric gaseous water of various species were also discussed. The key factor for the water collection and its conduction in the wheat plant is the information of contact angle hysteresis. In wheat, leaf rolling and its association with wetting property help the plant in water retention. Morphological adaptations, i.e., leaf erectness, grooves, and prickle hairs, also help in the collection and acquisition of water droplets by stem flows in directional guide toward the base of the plant and allow its rapid uptake. Morphological adaptation strengthens the harvesting mechanism by preventing the loss of water through shattering. Thus, wheat canopy architecture can be modified to harvest the atmospheric water and directional movement of water towards the root zone for self-irrigation. Moreover, these morphological adaptations are also linked with drought avoidance and corresponding physiological processes to resist water stress. The combination of these traits together with water use efficiency in wheat contributes to a highly efficient atmospheric water harvesting system that enables the wheat plants to reduce the cost of production. It also increases the yielding potential of the crop in arid and semi-arid environments. Further investigating the ecophysiology and molecular pathways of these morphological adaptations in wheat may have significant applications in varying climatic scenarios.

Keywords: Atmospheric gaseous water harvesting; Contact angle hysteresis; Drought; Morphological adaptations.

Fig. 1

Breakdown of freshwater (Shiklomanov 1993)

Fig. 2

Daily water consumption of wheat plants at different growth and development stages

Fig. 3

Wheat plant responses to water stress by complex mechanisms

Fig. 4

Leaf wettability mechanism by atmospheric water. An explanation of the basic processes involved in the collection of water on the leaf surface, absorption by the leaf surface, and transport of excess water to the root system of a wheat plant

Fig. 5

The schematic diagram shows the wetting of a solid surface. Contact angle (CA) of water droplet is described by Young’s equation (_ˠLA, _ˠSL, and _ˠSA show interfacial tensions at the boundaries between liquid (L), solid (S), and air (A)). The hysteresis of a water droplet on a tilted solid surface can be determined by measuring the advancing and receding angle of a water droplet (adapted from Barthlott et al. (2017)

Fig. 6

The schematic shows the characterization of wettability and contact angle of solid and liquid. FA stands for adhesive force and FC for cohesive force

Fig. 7

Rate of fog water collection and annual occurrence of foggy days in various countries (data source from Fessehaye et al. 2014)