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The upside-down water collection system of Syntrichia caninervis
Abstract
Desert plants possess highly evolved water conservation and transport systems, from the root structures that maximize absorption of scarce ground water1, 2, 3, 4, 5, to the minimization of leaf surface area6 to enhance water retention. Recent attention has focused on leaf structures that are adapted to collect water and promote nucleation from humid air7, 8, 9. Syntrichia caninervis Mitt. (Pottiaceae) is one of the most abundant desert mosses in the world and thrives in an extreme environment with multiple but limited water resources (such as dew, fog, snow and rain), yet the mechanisms for water collection and transport have never been completely revealed. S. caninervis has a unique adaptation: it uses a tiny hair (awn) on the end of each leaf to collect water, in addition to that collected by the leaves themselves. Here we show that the unique multiscale structures of the hair are equipped to collect and transport water in four modes: nucleation of water droplets and films on the leaf hair from humid atmospheres; collection of fog droplets on leaf hairs; collection of splash water from raindrops; and transportation of the acquired water to the leaf itself. Fluid nucleation is accomplished in nanostructures, whereas fog droplets are gathered in areas where a high density of small barbs are present and then quickly transported to the leaf at the base of the hair. Our observations reveal nature's optimization of water collection by coupling relevant multiscale physical plant structures with multiscale sources of water.
... For example, this kind of work can help understand the water collection processes of many plants. 16,[36][37][38][39][40][41][42] Furthermore, this work allows researchers and engineers to optimize the design for applications involving liquids on fibrous media, such as fog/dew collection, injection printing, or removal of toxic aerosols. Although this work demonstrated water droplets coalescing on pre-wetted superhydrophilic fibers in ambient air, we believe that similar directional transport can also appear in an aqueous environment, such as oil droplets on superoleophilic fibers submerged in water. ...
This study presents an unprecedented directional transport phenomenon during the coalescence of two droplets on a pre-wetted cylindrical fiber, where the larger droplet is pulled toward the smaller one. The magnitude of this effect often exceeds the gravitational pull, enabling coalescing droplets to climb up a vertical fiber. This occurs primarily because the viscous friction that the droplets experience is negatively correlated with the droplet size. We present a scaling relation and a mass-spring-damper model to explain the phenomenon, which shows good agreement with the experimental results. This research reveals an intriguing aspect of the coalescence dynamics of droplets on a pre-wetted fiber, offering a fresh perspective on the interfacial phenomena in droplet–fiber systems.
Access to a safe water supply is a human right (United Nations 2015). Fresh water sustains human life and is vital for human health.
Magnetically responsive microstructured functional surface (MRMFS), capable of dynamically and reversibly switching the surface topography under magnetic actuation, provides a wireless, noninvasive, and instantaneous way to accurately control the microscale engineered surface. In the last decade, many studies have been conducted to design and optimize MRMFSs for diverse applications, and significant progress has been accomplished. This review comprehensively presents recent advancements and the potential prospects in MRMFSs. We first classify MRMFSs into one-dimensional linear array MRMFSs, two-dimensional planar array MRMFSs, and dynamic self-assembly MRMFSs based on their morphology. Subsequently, an overview of three deformation mechanisms, including magnetically actuated bending deformation, magnetically driven rotational deformation, and magnetically induced self-assembly deformation, are provided. Four main fabrication strategies employed to create MRMFSs are summarized, including replica molding, magnetization-induced self-assembly, laser cutting, and ferrofluid-infused method. Furthermore, the applications of MRMFS in droplet manipulation, solid transport, information encryption, light manipulation, triboelectric nanogenerators, and soft robotics are presented. Finally, the challenges that limit the practical applications of MRMFSs are discussed, and the future development of MRMFSs is proposed.
Liquid mobility on fibers is critical to the effectiveness of fiber matrices in face masks, water harvesting and aerosol filtration, but is typically affected by Plateau-Rayleigh instability. However, the spontaneous flow within precursor films arising from this instability has been largely overlooked, particularly regarding its fundamental flow pattern and the potential for liquid mobilization. This study reveals the pivotal role of spontaneous flow on ribbon-like fibers in enhancing liquid transport. The non-axisymmetric curvature of these fibers induces long-wave instabilities, generating a sustained flow that enables film-wise transport over centimeter-scale distances at velocities of several millimeters per second. Using particle-image velocimetry, we uncover intricate hydrodynamics, including opposing flows within the film and organized vortices in the shear layer, driven by capillary effects at the liquid-vapor interfaces. Building on these insights, we demonstrate a network structure capable of achieving planar liquid transport over a 10 cm2 area. The ribbon-like fibers investigated exhibit the longest transport distances relative to biomimetic structures and aerodynamic propulsion. The unique transport dynamics and planar configuration of the fiber matrix offer substantial potential for advanced fiber-based liquid transport systems, with enhanced mass/heat transfer, laminar mixing and aerodynamic characteristics.
Energy conversion is a basic requirement for organic life. Many prokaryotes (archaea and bacteria) exploit electrochemical imbalances of inorganic elements or molecules for energy supply. These processes of chemoautotrophy are directly connected with modifications of inorganic chemical compounds creating the habitability of Earth in geological time scales and supporting eukaryotes with mineral nutrients in short time scales. Phototrophy—exploitation of photon energy—evolved in different forms in chemoautotrophs and extended as photosynthesis substantially the potentials for biological energy conversion together with an revolutionary change of environmental conditions by emission of oxygen-molecules. Consortia of prokaryotes and unicellular eukaryotes optimize as microbiomes the conversion of energy at boundaries between solid surfaces and water or air from hydrothermal vents to the intestine walls of animals. Embodied energy in multicellular organisms is transferred to mechanical energy as osmotic or—via motile biomolecules—muscle forces. Motion requires counterforces provided by elastic tissues or exo- and endoskeletons.
Drop–fiber interactions are fundamental to the operation of technologies such as atmospheric fog capture, oil filtration, refrigeration, and dehumidification. We demonstrate that by twisting together two fibers, a sliding drop’s flow path can be controlled by tuning the ratio between its size and the twist wavelength. We find both experimentally and numerically that twisted fiber systems are able to asymmetrically stabilize drops, both enhancing drop transport speeds and creating a rich array of new flow patterns. We show that the passive flow control generated by twisting fibers allows for woven nets that can be “programmed” with junctions that predetermine drop interactions and can be anticlogging. Furthermore, it is shown that twisted fiber structures are significantly more effective at capturing atmospheric fog compared to straight fibers.
Although the desert moss Syntrichia caninervis Mitt. is extremely desiccation tolerant, it still requires water and photosynthates for growth. The ecological significance of the leaf angle in maintaining a balance between water and light availability is critical to its survival. Active leaf repositioning balances water and light availability following rehydration. S. caninervis can adjust leaf angles from a steep (84-69 degrees) to a stable level at 30 degrees within 7 s after rehydration, obtaining maximum net photosynthetic gain at a shoot relative water content of similar to 60%. Leaf morphological characters, (leaf hair points, surface papillae and costal anatomy) and ultrastructural changes (chloroplast reordering and loss of lipid reserves as shown by changes in osmiophilic globules) were linked to rapid leaf spreading, water gain and sunlight reflectivity of leaves during rehydration. The high 377.20 +/- 91.69 (cm(2) g(-1)) surface area to mass ratio was a major factor in facilitating the rapid response to rewetting. Hyaline cells of the leaf base absorbed water, swelled and forced the leaf away from the stem as soon as rehydration commenced. Loss of leaf hair points retards leaf angle adjustment during rehydration.
Fog represents a large, untapped source of potable water, especially in arid climates. Numerous plants and animals use textural as well as chemical features on their surfaces to harvest this precious resource. In this work, we investigate the influence of surface wettability characteristics, length scale, and weave density on the fog harvesting capability of woven meshes. We develop a combined hydrodynamic and surface wettability model to predict the overall fog collection efficiency of the meshes and cast the findings in the form of a design chart. Two limiting surface wettability constraints govern re-entrainment of collected droplets and clogging of mesh openings. Appropriate tuning of the wetting characteristics of the surfaces, reducing the wire radii, and optimizing the wire spacing all lead to more efficient fog collection. We use a family of coated meshes with a directed stream of fog droplets to simulate a natural foggy environment and demonstrate a five-fold enhancement in the fog-collecting efficiency of a conventional polyolefin mesh. The design rules developed in this work can be applied to select a mesh surface with optimal topography and wetting characteristics to harvest enhanced water fluxes over a wide range of natural convected fog environments.
Multiple biological structures have demonstrated fog collection abilities, such as beetle backs with bumps and spider silks with periodic spindle-knots and joints. Many Cactaceae species live in arid environments and are extremely drought-tolerant. Here we report that one of the survival systems of the cactus Opuntia microdasys lies in its efficient fog collection system. This unique system is composed of well-distributed clusters of conical spines and trichomes on the cactus stem; each spine contains three integrated parts that have different roles in the fog collection process according to their surface structural features. The gradient of the Laplace pressure, the gradient of the surface-free energy and multi-function integration endow the cactus with an efficient fog collection system. Investigations of the structure-function relationship in this system may help us to design novel materials and devices to collect water from fog with high efficiencies.
The wetting and spreading of liquids on solids is frequently encountered in the chemical industry. This paper presents some simple but powerful thermodynamic concepts that can be taught in a 1-hour lecture on wetting and spreading. We approach the subject through the theme of the minimization of free energy - a concept with which chemical engineering students are well acquanted.
It is postulated that the Australian angiosperm flora ins derived from a sample of a one-time world flora of about 180 families that entered Australia by a land bridge from Asia. Many of the genera that entered still persist. New genera evolved in all habitats, many from lineages which were adapted to soils of low fertility determined primarily by phosphate level. Soil parent materials with the highest phosphate content are derived mainly from the Tertiary basalts in the east and support rainforests (except in cold regions). Soil phosphate levels decrease from east to west across the continent. The number of rainforest genera in any community is usually correlated with soil P. The converse holds for xeromorphic genera. Some rainforest genera therefore are more readily adapted to aridity than to low fertility conditions. Expansion and contraction of the rainforest is determined partly by climate and partly by soil fertility levels. A sudden expansion of the rainforest in the Oligocene occurred when the basalt flows covered part of eastern Australia. Since that time the rainforests have contracted, partly as a result of the removal of basaltic material and partly because of the development of colder climates in the ranges. The absence of rainforest and the paucity of rainforest genera in southwest Western Australia are accounted for by low fertility levels rather than by a decimation of rainforest genera by a past dry climate. Xermorphy, a result of high lignification, heavy cutinization, silicification, or a combination of these may occur in rainforest species. Adaptation to low fertility accentuates xeromorphic characters through a reduction in leaf size. The low fertility xeromorphs are not xerophytes. Anatomical features have little significance in their survival, which is determined by the ability of the plants to withstand long periods of mineral starvation. Experimental work indicates that the degree of xeromorphy can be reduced in many taxa by the addition of phosphorus and nitrate; four different types of leaf response have been identified.
An impact-type Joss-Waldvogel disdrometer (JWD), a two-dimensional video disdrometer (2DVD), and a laser optical OTT Particle Size and Velocity (PARSIVEL) disdrometer (PD) were used to measure the raindrop size distribution (DSD) over a 6-month period in Huntsville, Alabama. Comparisons indicate event rain totals for all three disdrometers that were in reasonable agreement with a reference rain gauge. In a relative sense, hourly composite DSDs revealed that the JWD was more sensitive to small drops (<1 mm), while the PD appeared to severely underestimate small drops less than 0.76 mm in diameter. The JWD and 2DVD measured comparable number concentrations of midsize drops (1-3 mm) and large drops (3-5 mm), while the PD tended to measure relatively higher drop concentrations at sizes larger than 2.44 mm in diameter. This concentration disparity tended to occur when hourly rain rates and drop counts exceeded 2.5 mm h(-1) and 400 min(-1), respectively. Based on interactions with the PD manufacturer, the partially inhomogeneous laser beam is considered the cause of the PD drop count overestimation. PD drop fall speeds followed the expected terminal fall speed relationship quite well, while the 2DVD occasionally measured slower drops for diameters larger than 2.4 mm, coinciding with events where wind speeds were greater than 4 m s(-1). The underestimation of small drops by the PD had a pronounced effect on the intercept and shape of parameters of gamma-fitted DSDs, while the overestimation of midsize and larger drops resulted in higher mean values for PD integral rain parameters.
We use high-speed video imaging to study the capillary-driven motion of a micro-droplet along the outside of a pre-wetted conical fiber. The cones are fabricated on a glass-puller with tip diameters as small as 1 μm, an order of magnitude smaller than in previous studies. The liquid is fed through the hollow fiber accumulating at the fiber tip to form droplets. The droplets are initially attached to the opening as they grow in size before detaching and traveling up the cone. This detachment can produce a transient oscillation of high frequency. The spatial variation of the capillary pressure drives the droplets towards the wider side of the cone. Various liquids were used to change the surface tension by a factor of 3.5 and viscosity by a factor of 1500. Within each droplet size and viscous-dissipation regime, the data for climbing speeds collapse on a single curve. Droplets traveling with and against gravity allow us to pinpoint the absolute strength of the driving capillary pressure and viscous stresses and thereby determine the prefactors in the dimensionless relationships. The motions are consistent with earlier results obtained from much larger cones. Translation velocities up to 270 mm/s were observed and overall the velocities follow capillary-viscous scaling, whereas the speed of the fastest droplets is limited by inertia following their emergence at the cone tip.
Leaf hydrophobicity and water droplet retention are important functional traits among plant species and may be important selective strategies to increase water availability to root systems in arid and semi-arid environments. Hydrophobic canopies may decrease rainfall interception and increase throughfall to the soil. Leaf angle may also influence the ability of water droplets to channel off leaf surfaces. Water droplets may have a greater ability to drain off leaf surfaces with steeper leaf angles which decrease rainfall interception and increase throughfall to the soil. This study examined the relationships between leaf angle, leaf hydrophobicity, and water droplet retention in 11 species from a semi-arid region of Colorado in the western United States. Leaf hydrophobicity of the adaxial and the abaxial leaf surface was measured by calculating the contact angle between a water droplet and the leaf surface. Water droplet retention was measured as the angle at which a water droplet begins to move as a leaf is incrementally tilted from 0° to 90°. Leaf hydrophobicity was greater than leaf angle for 9 species and similar for 2 species. Leaf angle was greater than water droplet retention on the adaxial leaf surface for 8 species and similar for 3 species. Leaf angle was greater than water droplet retention on the abaxial leaf surface for 7 species and similar for 2 species. The relationship between leaf angle and leaf hydrophobicity and the relationship between leaf angle and water droplet retention were weak; however, the relationship between leaf hydrophobicity and water droplet retention was stronger. Results indicate that intercepted water droplets during a rainfall event will likely drain off the leaf surfaces from a majority of the species examined and contribute to throughfall because leaf angle is greater than water droplet retention in these species. The relationship between leaf angle and canopy hydrophobicity may be a significant influence on hydrological processes in arid and semi-arid regions.
The region at Albuquerque differs from that of Tucson in having about two-thirds as much rainfall and much lower winter temperatures. The soil of the mesa is fluviatile in origin and very diverse in composition. The hardpan layer prominent at Tucson is not well developed. The winter annuals and the larger shrubs and cacti are absent. Most of the plants are perennial herbs. The root systems generally penetrate rather deeply, but often have prominent laterals near the surface of the soil. The cacti and a few of the shrubs have a very superficial root system. The larger cacti show a differentiation into anchorage and absorptive roots. The plants of arroyo sides have prominent tap roots varying in length with the height of the plant above the bottom of the arroyo. Storage roots are uncommon and are more characteristic of the moister situations. Vegetative reproduction from roots is common in the plants of unstable soil. While the causes of root variation can be accurately determined only under laboratory conditions, two factors exert a very evident influence, variation in the penetrability of the soil and in its moisture content. The roots of the plants of an association are grouped into rather definite layers, so that root competition is lessened. The composition of an association is probably determined largely by root competition.
The biological soil crusts (BSCs) in the Gurbantunggut Desert, the largest fixed and semi-fixed desert in China, feature moss-dominated BSCs, which play an indispensable role in sand fixation. Syntrichia caninervis Mitt. (S. caninervis) serves as one of the most common species in BSCs in the desert. In this study we examined the morphological structure of S. caninervis from leafy gametophyte to protonema using light and scanning electron microscopy (SEM). We also examined the relationships between the morphological structure of S. caninervis and environmental factors. We found that: (1) this moss species is commonly tufted on the sand surface, and its leaves are folded upwards and twisted around the stem under dry conditions; (2) the cells on both upper and lower leaf surfaces have C-shaped dark papillae, which may reflect sunlight to reduce the damage from high temperature; (3) the leaf costa is excurrent, forming an awn with forked teeth; and (4) the protonema cells are small and thickset with thick cell walls and the cytoplasm is highly concentrated with a small vacuole. In addition, we also found that the protonema cells always form pouches on the tip of the mother cells during the process of cell polarization. Our results suggest that S. caninervis has, through its life cycle, several morphological and structural characteristics to adapt to dry environmental conditions. These morphological features of S. caninervis may also be found in other deserts in the world due to the world-wide distribution of the species.