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Theoretical and experimental contact angles, roughness, and the areal fraction of intact wax regions in different leaves
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Deciduous broad-leaf trees survive and prepare for winter by shedding their leaves in fall. During the fall season, a change in a leaf’s wettability and its impact on the leaf-fall are not well understood. In this study, we measure the surface morphology and wettability of Katsura leaves from the summer to winter, and reveal how leaf structural cha...
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... When the vertical downward force of a hanging drop by gravity and the vertical component of water inflow velocity exceeds the adhesive force, the hanging drop detaches from the plant surfaces. The adhesive force is partly determined by plant surface hydrophobicity, which is related to the roughness of the plant surface, the density of trichomes and chemical wax, and water viscosity related to water temperature and concentration of nutrients in the water (Gart et al., 2015;Holder, 2020;Kang et al., 2018;Konrad et al., 2013;Nanko et al., 2013). Plant surfaces with higher hydrophobicity can maintain lighter hanging drops and generate smaller drops than those with lower hydrophobicity (Konrad et al., 2013;Nanko et al., 2013). ...
Throughfall is a significant majority of the total precipitation reaching the ground in forested areas. This study revealed biotic and abiotic factors influencing the throughfall generation process, with the throughfall partitioning into free throughfall, splash throughfall, and canopy drip created at foliar surface drip points (FSDPs) and occasional woody surface drip points (O‐WSDPs), utilizing machine learning. Using a large‐scale rainfall simulator, throughfall drops were simultaneously measured at 19 locations under a mix of deciduous and coniferous tree species in both foliated and unfoliated states. Random forest modeling showed that biotic factors, such as foliage amount, primarily affected the development and volume fraction of canopy drip in foliated trees. In contrast, for unfoliated trees, canopy drip volume fraction was mainly influenced by abiotic factors, including drop size and kinetic energy of open rainfall. The formation and volume fraction of splash throughfall were primarily influenced by abiotic factors for both foliated and unfoliated trees. From the comparison between the foliated and unfoliated states, the generation process of canopy drip was separately clarified between FSDPs and O‐WSDPs. More and larger canopy drip was generated by more foliage with a more wetted canopy with less fluctuation at the FSDPs, whereas a less wetted canopy and/or higher drop impact energy generated more and larger canopy drip at O‐WSDPs. This study underscores the importance of canopy structure and meteorological conditions in determining throughfall partitioning. The findings contribute to a nuanced understanding of rainwater redistribution in forest ecosystems.
... The flexible rigidity depends on the the elastic modulus E and the second moment of area I. 143 The second moment of area I comprises of the width b and thickness h of the cantilever, where 144 I = bh 3 12 . The EI values of these cantilevers were experimentally calculated for the normal and 145 grid cantilevers respectively (Table I). ...
... Plant leaves have many biological factors that can alter surface characteristics (i.e. hydrophobicity [2], shape, and surface topography [3,4]), which affect the canopy water storage capacity [2]. Furthermore, the geometry and material properties of the leaf can differ across species and position in the canopy [4]. ...
In this study, we investigated the dynamics of a droplet impacting and oscillating a polycarbonate cantilever beam of nine varying lengths. We analyzed the cantilever's damping and vibration frequency in relation to a resonance length, where the frequencies of the droplet and the cantilever are equal. In the pre-resonance length, the beam vibrates at a frequency higher than that of the droplet. Upon reaching resonance, the frequencies of both the droplet and the cantilever align, and the cantilever is out of phase with the oscillation of the droplet's apex. This leads to increased damping rates. At this resonance length, the droplet's force and the direction of the cantilever oppose each other. When the cantilever length exceeds the resonance length, it synchronize more with the droplet apex. This alignment allows the droplet force and the cantilever to work in phase. Our findings provide fundamental insights into the damping effect of droplet impacts on elastic surfaces around resonance.
... It is an important fact that mosses are pioneering plants, which often inhabit wastelands and then transform the substrate, allowing more demanding plants to settle, and that they create an environment with high water retention properties. The research should also be extended in the future to take into account the seasonal changes, similarly as it this is done for leaves (Kang et al., 2018). ...
The forest has a high water retention capacity, which is due to dead wood but also to a layer of moss, forming clusters in the lower forest floor. Mosses use rhizoids to collect water from the soil, but they also use their aboveground parts to collect water in the form of vapour or raindrops. The aim of the present work was to investigate the impact of initial humidity on water retention capacity of fresh samples and maximum water capacity for dry samples. The research material used in the present study was collected in the Olkusz Forest District. The samples were cut into equal pieces of the same size. Each sample was weighed before and after rainfall simulation in laboratory conditions. The samples were divided into fractions of stems, rhizoids, and soil. The performed analyses demonstrated that the water retention capac− ity of moss is extremely important for the water cycle. The average sample capacity is 0.58 [g/g], which translates into 24% of the total rainfall. As much as a third of the rainfall is rainfall is retained by mosses that grow on the lower layer of the forest, which makes them an important part of the water cycle in nature. The experiments have additionally shown that the higher the initial moisture, i.e. the more water in the fresh moss samples collected with the lump of earth, the higher the maximum water retention capacity. The dependence of the initial moisture on the components of the sample structure is explained by 43.22% variation. As much as 56.78% of the variability of the initial moisture content may depend on other factors that were not included in this study. These may include a different number of rhizoids, but also the degree of their binding/bonding of the soil. On the other hand, the lack of correlation of the water retention capacity, either the current one or that related to the dried weight of the sample, with the structural components of the sample tells us a lot about the complexity of the link between the moss and the soil via the rhizoids. The results obtained in the present study are in line with the research on the hydrological prop− erties of forest ecosystems; they also indicate that the role of moss in the forest is very impor− tant, but not yet fully understood. ABSTRACT original paper Water retention capacity of red−stemmed feathermoss Pleurozium schreberi Mitt.
... In different climatic zones, pear leaves in the early growth period were more hydrophobic than those in the late growth period, attributed to significant changes in surface wax composition (Gao et al., 2018). In addition, reduced surface wax composition allowed summer laurel leaves to also exhibit greater hydrophobicity than fall leaves due to fall climate (Kang et al., 2018). Changes in surface microstructure also influence the alternating changes in wettability of leaves throughout the year. ...
A wide variety of abundant plant leaves exist in nature, and the wettability of their surfaces is formed to adapt to diverse external environments. In this paper we will focus on the factors influencing the wettability of various plant leaves prevalent in nature. And we hope to investigate the interfacial problems of plants from a mechanical point of view. It is found that there are many factors affecting the surface wettability of leaves, such as chemical composition, surface microstructures, hierarchical structures, and growth age. Different influencing factors have different contributions to the change of surface wettability. The surface wax composition influences the surface wettability from a chemical point of view while the hierarchical structure consisting of nanostructures and micron structures also influences the wettability from a structural point of view. Also as the growth age of the plant increases, there is a combined effect on the chemical composition and microstructure of the leaves. Then we discuss the surface/ interface mechanics of droplets on various plant leaves and analyze the wetting properties of droplets on different substrates. Finally, we hope that the surface/ interface mechanics of plant leaves may be systematically utilized in the future for the preparation of multifunctional biomimetic materials, realizing the crossover of chemistry, biology, mechanics, and other materials science fields.
... 23,25 Other plant waxes documented within the literature to have a tubular structure include ginkgo 26 and katsura. 27 Horsetail also has nano-scale surface roughness, but from silicon dioxide crystals. 28 In contrast, maple contains wax platelets 29 and the morphology of carnauba is not documented within the literature. ...
... On the natural leaf surfaces, ginkgo and katsura waxes have both exhibited near-superhydrophobicity. 27,32 With maple wax achieving one of the lowest contact angles in the study (Fig. 6), and cedar wax achieving one of the highest, a very general link can be drawn between the relative abundance of co-crystallizing compounds and the contact angle of the re-crystallized waxes. However, this is not the only contributing factor, as smoketree wax has a slightly higher contact angle than cedar wax but a much lower relative abundance of co-crystallizing compounds. ...
Novel superhydrophobic coatings, that are both biodegradable and biosourced, have the potential to revolutionize the water-repellent coating industry. Here, water-repellent coatings were prepared from commercially unavailable plant waxes, isolated using solvent extraction and characterized using DSC, GC-MS and DLS. In the first stage, a plant survey was conducted to identify an ideal plant source for the final spray, in which Whatman filter paper was submerged in a wax-solvent solution with recrystallization occurring upon air-drying. In the second stage, aqueous, PFC-free wax dispersions were prepared, coated onto textiles (cotton and polyester), and heat-treated with a home drying machine to allow for the spreading and recrystallization of the waxes. In both stages, SEM visualization verified the coating's morphology, and contact angle measurements showed them to be superhydrophobic. It was concluded that, using less coating material than commercial coatings, high-performing petroleum-free coatings could be made and applied onto textiles of various polarities.
... In drier environments, leaves tend to reduce their leaf area, increase the cuticular waxes and trichomes and reduce the stomatal density to reduce water deficits (Ennajeh et al., 2006;Kosma et al., 2009;Saneoka & Ogata, 1987;Zhao et al., 2015); thus, these traits play a pivotal role in protecting plants from abiotic stresses, such as drought. Other leaf surface traits (e.g., wettability, water adhesion, interception and retention) also can respond to changes in water availability and affect the leaf water loss or the foliar water uptake (FWU; Cavallaro et al., 2022;Fogg, 1947;Kang et al., 2018;Lenz et al., 2022). Some studies have argued that high wettability can negatively affect the plant function (e.g., increase pathogen establishment and reduce CO2 diffusion), such that wet environment should be select for less wettable leaves (Sase et al., 2008). ...
Water availability is one of the factors affecting plant growth and development, especially in arid and semiarid environments. Changes in precipitation due climate change alter water availability to plants impacting on plant physiology. Numerous studies have focused on plant response to reduced precipitation and less on the effects of increased precipitation. The main objective of this study was to evaluate biophysical and physiological leaf traits in response to experimental water addition in four dominant shrubs and one grass species in a Patagonian steppe, during the dry season. The experiment consisted of two treatments: control and water addition, increasing the average annual rainfall by 25% during 6 years. We measured leaf wettability, water status, transpiration, photosynthesis, stomatal conductance, water use efficiency and foliar water uptake (FWU). In addition, we determined the phenotypic plasticity index of these evaluated traits. We expected lower FWU and higher transpiration and photosynthesis rates due changes in leaf surface properties under water addition treatment. All study species responded significantly to treatment with higher loss of water per transpiration and lower FWU. Also, all species increased photosynthesis rate and water use efficiency (WUE). However, water potential and leaf wettability did not change with higher precipitation. Thus, higher phenotypic plasticity was observed in functional than in morphological traits. Since functional traits were more sensitive than leaf surface traits, plants may quickly take advantage when environmental conditions tend to be more favourable to growth. Our findings suggest that plants of Patagonian steppe have adaptive ability to respond to environmental changes through plastic responses.
... As the thin lamella moves along a convex surface, it becomes unstable and may generate and eject more splashes. Such splashes could affect both water retenion on plants [37,38] and spore dispersal [39], which leads to interesting questions and implications. ...
In nature, high-speed rain drops often impact and spread on curved surfaces e.g. tree leaves. Although a drop impact on a surface is a traditional topic for industrial applications, drop-impact dynamics on curved surfaces in natural situations are less known about. In the present study, we examine the time-dependent spreading dynamics of a drop onto a curved hydrophobic surface. We also observed that a drop on a curved surface is spreads farther than one on a flat surface. To understand the spreading dynamics, a new analytical model is developed based on volume conservation and temporal energy balance. This model converges to previous models at the early stage and in the final stage of droplet impact. We compared the new model with measured spreading lengths on various curved surfaces and impact speeds, which resulted in good agreement.
... Epicuticular wax crystals can be reduced or absent in plants growing under low light conditions (Hallam, 1970) or under elevated air humidity (Koch et al., 2006). Seasonal changes of epicuticular wax load and composition are widespread and have been attributed to leaf ontogeny (Jetter and Schäffer, 2001), temperature and water availability (Ziv et al., 1982;Jordan et al., 1983), and erosion of wax crystals over time (Neinhuis and Barthlott, 1998;Kang et al., 2018). Multiple studies report an increase in leaf wettability for broad-leaved trees towards the later part of the growth season, namely with increasing leaf age (Neinhuis and Barthlott, 1998;Tranquada and Erb, 2014;Kang et al., 2018;Xiong et al., 2018). ...
... Seasonal changes of epicuticular wax load and composition are widespread and have been attributed to leaf ontogeny (Jetter and Schäffer, 2001), temperature and water availability (Ziv et al., 1982;Jordan et al., 1983), and erosion of wax crystals over time (Neinhuis and Barthlott, 1998;Kang et al., 2018). Multiple studies report an increase in leaf wettability for broad-leaved trees towards the later part of the growth season, namely with increasing leaf age (Neinhuis and Barthlott, 1998;Tranquada and Erb, 2014;Kang et al., 2018;Xiong et al., 2018). ...
Water shedding from leaves is a complex process depending on multiple leaf traits interacting with rain, wind and air humidity, and with the entire plant and surrounding vegetation. Here, we synthesise the current knowledge of the physics of water shedding with implications for plant physiology and ecology. We argue that the drop retention angle is a more meaningful parameter to characterise the water shedding capacity of leaves than the commonly measured static contact angle. The understanding of the mechanics of water shedding is largely derived from laboratory experiments on artificial rather than natural surfaces, often on individual aspects such as surface wettability or drop impacts. In contrast, field studies attempting to identify the adaptive value of leaf traits linked to water shedding are largely correlative in nature, with inconclusive results. We make a strong case for taking the hypothesis-driven experimental approach of biomechanical lab studies into a real-world field setting to gain a comprehensive understanding of leaf water shedding in a whole-plant ecological and evolutionary context.
... where R is the universal gas constant, T is the temperature, p vapor is the actual vapor pressure, and p sat is the saturated vapor pressure This relation explains that the droplet nucleation easily occurs on a hydrophilic surface (cos θ Equil > 0) at any groove sizes (r) in saturated air (p vapor /p sat > 1). Hierarchical double-layer roughness (i.e., nanowax and microbumps) is typical for leaf surfaces in nature (e.g., Lotus leaf [16,17], Katsura tree leaf [18], and a recent review in [19]). Especially, the nanowax might provide the groove lengthscale to initiate the droplet nucleation. ...
... Three cases are presented: a single semicylinder, a single prolate semi-ellipse, and a single hair. These structures are inspired by the microstructures found on real plant leaves (Circular epidermal bumps in Cercidiphyllum japonicum [18]; prolate bumps in Viola tricolor [19]; hair-like structures in Phaseolus vulgaris [19]). As shown in Fig. 2(B), vapor concentration contours are pushed up quite a bit with elongated prolate or hair-like structures. ...
... Summary of normalized vapor flux around different single bumps FIG. 2. (A) Bump structures on plant surfaces (Images from left to right are Cercidiphyllum japonicum[18]; Viola tricolor[19]; Phaseolus vulgaris ...
Drop condensation and evaporation as a result of the gradient in vapor concentration are important in both engineering and natural systems. One of the interesting natural examples is transpiration on plant leaves. Most of the water in the inner space of the leaves escapes through stomata, whose rate depends on the surface topography and a difference in vapor concentrations inside and just outside of the leaves. Previous research on the vapor flux on various surfaces has focused on numerically solving the vapor diffusion equation or using scaling arguments based on a simple solution with a flat surface. In this present work, we present and discuss simple analytical solutions on various 2D surface shapes (e.g., semicylinder, semiellipse, hair). The method of solving the diffusion equation is to use the complex potential theory, which provides analytical solutions for vapor concentration and flux. We find that a high mass flux of vapor is formed near the top of the microstructures while a low mass flux is developed near the stomata at the leaf surface. Such a low vapor flux near the stomata may affect transpiration in two ways. First, condensed droplets on the stomata will not grow due to a low mass flux of vapor, which will not inhibit the gas exchange through the stomatal opening. Second, the low mass flux from the atmosphere will facilitate the release of highly concentrated vapor from the substomatal space.
