The effects of leaf roughness, surface free energy and work of adhesion on leaf water drop adhesion.

Huixia Wang,Yangyang Li,Hui Shi,Yanhui Wang,Yang Gan

doi:10.1371/journal.pone.0107062

Abstract

The adhesion of water droplets to leaves is important in controlling rainfall interception, and affects a variety of hydrological processes. Leaf water drop adhesion (hereinafter, adhesion) depends not only on droplet formulation and parameters but also on the physical (leaf roughness) and physico-chemical (surface free energy, its components, and work-of-adhesion) properties of the leaf surface. We selected 60 plant species from Shaanxi Province, NW China, as experimental materials with the goal of gaining insight into leaf physical and physico-chemical properties in relation to the adhesion of water droplets on leaves. Adhesion covered a wide range of area, from 4.09 to 88.87 g/m2 on adaxial surfaces and 0.72 to 93.35 g/m2 on abaxial surfaces. Distinct patterns of adhesion were observed among species, between adaxial and abaxial surfaces, and between leaves with wax films and wax crystals. Adhesion decreased as leaf roughness increased (r = −0.615, p = 0.000), but there were some outliers, such as Salix psammophila and Populus simonii with low roughness and low adhesion, and the abaxial surface of Hyoscyamus pusillus and the adaxial surface of Vitex negundo with high roughness and high adhesion. Meanwhile, adhesion was positively correlated with surface free energy (r = 0.535, p = 0.000), its dispersive component (r = 0.526, p = 0.000), and work of adhesion for water (r = 0.698, p = 0.000). However, a significant power correlation was observed between adhesion and the polar component of surface free energy (p = 0.000). These results indicated that leaf roughness, surface free energy, its components, and work-of-adhesion for water played important roles in hydrological characteristics, especially work-of-adhesion for water.

Highlights

The retention of water drops by leaves can be measured as the amount of surface water per unit leaf area at a point which additional water can no longer be retained and starts to drip off [1]
Among the 60 species analyzed, the adhesion was significantly greater on the adaxial surface than on the abaxial surface for 24 species (Table 1, t-test, p,0.05)
We propose that the high adhesion of the abaxial surface of H. pusillus and the adaxial surface of V. negundo is caused by capillary action or the ‘‘segregating strategy’’ (e.g., Fig. 2E), that segregated water into patches based on water drawn along the trichomes or rugose surface

Summary

Introduction

The retention of water drops by leaves can be measured as the amount of surface water per unit leaf area at a point which additional water can no longer be retained and starts to drip off [1]. Leaf water drop adhesion (hereinafter, adhesion) varies among species from 0.1 to 500 g/m2 [1,2,3]. The spread of liquids on a particular leaf surface is dependent on the leaf wettability or hydrophobicity of the leaf itself [10]. These properties vary among species and are, to some extent, influenced by factors such as leaf age [11,12], leaf surface (adaxial/abaxial) [12], epiphytic microorganisms [13], and environmental conditions [14]

Methods

Results

Discussion

Conclusion