Leaves Capture Water

Biological Strategy

Bromeliads

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Distribute Liquids

Liquids include water, as well as body fluids such as blood, gastric juices, nutrient-laden liquids, and more. To survive, many living systems must move such liquids within themselves or between locations. Because of their properties, liquids tend to disperse unless they are confined in some way. To address this, living systems have strategies to confine fluids for transport, and to overcome barriers such as gravity, friction, and other forces. Some of these same barriers also provide opportunities. Trees and giraffes face the same challenge: how to move fluids (water and blood, respectively) upward against gravity. But their strategies are quite different. The tree moves water using capillary action and evaporation, possibly due to water’s properties of polarity and adhesion. The giraffe’s tight skin provides pressure to assist in blood circulation. and keep blood from pooling in the legs.

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Store Liquids

Many living systems must store liquids, such as water or nectar, so that it is available over long periods of time, including when moisture levels are low. Because of their properties, liquids tend to disperse unless they are confined in some way. Each liquid has its own unique properties. For example, water is polar, exhibiting a strong negative charge on one side of the molecule and a strong positive charge on the other. Living systems have strategies to confine fluids by taking advantage of these properties. A good example of taking advantage of water’s polarity is using materials that repel water. In doing so, a living system can keep water on one side of a barrier, such as a membrane.

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Capture, Absorb, or Filter Liquids

The most common liquid used by living systems is water, which they require to survive. But there are many other liquids that provide nourishment, play a role in defense mechanisms, or serve other purposes. Water varies in its availability; it is sometimes plentiful and sometimes very scarce or only available as fog or mist. To minimize the energy required to capture, absorb, or filter liquids, living systems have strategies that take advantage of the unique properties of the given liquid. For example, water moves from a gaseous to liquid state when it encounters a surface colder than the air. Plants in forests that experience fog and clouds more than rain have strategies that condense liquid water from moist air.

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Capture, Absorb, or Filter Chemical Entities

Living systems often require chemical elements and chemical compounds, including complex sugars, proteins, and odor-making compounds, to perform critical activities. These compounds exist in various states–solid, liquid, and gas–and are ubiquitous in soil, water, and air. This requires that living systems not only have ways to capture, absorb, or filter them, but also ways to differentiate among them, selecting those that are valuable or harmful. For example, mangrove trees live with their roots in salty water and sediments. Various mangrove species have different strategies for removing salt from the water they take in so that their tissues can use the fresh water.

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Move in/on Solids

To obtain needed resources or escape predators, some living systems must move on solid substances, some must move within them, and others must do both. Solids vary in their form; they can be soft or porous like leaves, sand, skin, and snow, or hard like rock, ice, or tree bark. Movement can involve a whole living system, such as an ostrich running across the ground or an earthworm burrowing through the soil. It can also involve just part of a living system, such as a mosquito poking its mouthparts into skin. Solids vary in smoothness, stickiness, moisture content, density, etc, each of which presents different challenges. As a result, living systems have adaptations to meet one, and sometimes multiple, challenges. For example, some insects must be able to hold onto both rough and slippery leaf surfaces due to the diversity in their environment.

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Flowering Plants

Clade Angiosperms (“receptacle seed”): Dandelions, oaks, grasses, cacti, apples

With 416 families containing some 300,000 known species, angiosperms are the most diverse group of plants, and they can be found around the globe in a wide variety of habitats. They are characterized by seeds that grow enclosed in ovaries, which are enclosed in flowers. The floral organs then develop into fruits of myriad kinds and dimensions, from simple seed casings on maples to elaborate fleshy growths like papayas. The oldest flower known from fossils, Montsechia vidalii, appeared during the Jurassic Period 130 million years ago. They are the primary food source for herbivorous animals, which in turn makes them the indirect food source for carnivores as well.

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The leaves of some bromeliads capture water and nutrients in a storage tank via hydrophobic leaf surfaces.

Some plants included in the family Bromeliaceae, such as pineapples, have a unique surface on their leaves that enables them to collect water in a central tank where it can be absorbed and utilized. This does not occur in all bromeliads, but just those that grow in areas where there may be less access to nutrients (such as hanging on trees where they rely on nutrients dissolved in rainwater).

The leaves of these types of bromeliads have a convex shape, meaning that they form a curved arch away from the surface they grow on. This shape allows water to drip downward into the central tank, pulled by the force of gravity. The interior, concave shape of the leaf also aids in the gathering and shuttling of water. The edges of the leaf bend upward, creating a structure that looks like a miniature half-pipe. This water collection is helpful for the bromeliad because it enables the plant to collect life-sustaining nutrients from the standing water over a longer period of time.

The leaves of bromeliads are also coated in small surface cells that are raised like bumps, known as trichomes. These “bumpy” cells have tiny hairs that catch water as it drops. The hairs increase in number as the water moves closer toward the base of the leaves, where the tank is formed. The small hairs on the leaves are coated in tiny, hydrophobic (i.e., water-repelling) wax crystals. Because the wax crystals do not absorb any water, the water rolls off of them until it collects in the central tank. The hairs are several millimeters higher than the outer surface of the leaf and thus hold the water above the leaf itself, keeping water from contacting the leaf surface proper. This is important because the surface proper is not necessarily covered in the same hydrophobic wax as the hairs, and thus water could “stick” to this surface if it came in contact with it.

As the hydrophobic properties of the leaves direct water downward to the plant’s center, a pool forms, acting as a water reserve of dissolved nutrients.

This summary was contributed by Ashley Meyers.

Epiphytes Capture Nutrients

Bromeliads

Bromeliads capture water and spawn a small community whose collective roles lead to nutrient supply for the epiphytic plants.

Last Updated March 27, 2017

References

“Hydrophobic leaf surfaces of Bromeliaceae possess a highly irregular microrelief, thereby reducing the adhesion and spread of water on the leaf blade. Hydrophobic trichome layers occur on the abaxial leaf blade surfaces of many mesic Type 1 pitcairnioids and, as these species exhibit the putative primitive ecological condition, water repellency appears to have been an important condition in early Bromeliaceae. The trichomes of Type 4 species are specialized for the alternative function of water and nutrient absorption from a water-filled tank, with epicuticular wax powders employed by some species to shed water from the leaf blades. Hydrophobic trichome layers and wax powders could potentially obstruct pathogens and particulates, aid in self-cleaning, and/or maintain gas exchange during wet weather.” (Pierce et al. 2001:1379)

Journal article

Hydrophobic Trichome Layers and Epicuticular Wax Powders in Bromeliaceae

American Journal of Botany | 02/02/2007 | Simon Pierce, Kate Maxwell, Howard Griffiths, Klaus Winter

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Reference

“So successful are these techniques for sending seeds up into the canopy that the massive branches of many forest trees are often densely lined with squatters. These are known as epiphytes and among the commonest are bromeliads. They anchor themselves by wrapping their roots around the branch. Their long leaves grow in a tight rosette around their central bud and channel rain water down to it so that the rosette fills and forms a small pond.” (Attenborough 1995:166)

Book

The Private Life of Plants

21/08/1995 | David Attenborough

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Reference

“Leaves with waxy trichomes are extremely water repellent… The crucial factor of superhydrophobicity in…leaves is given by the hairs, several hundreds of micrometres high, which are superimposed by a layer of small hydrophobic wax crystals… These surfaces are superhydrophobic, but the water droplets do not penetrate between the hairs; thus, small particles from the leaf surface would not be removed by rinsing with water… Such hairy systems may also be extremely useful for underwater systems because they minimize the wetted area of immersed surfaces and therefore may greatly reduce drag, as well as the rate of bio?lm formation, and are of great interest in biomimetics.” (Koch and Barthlott 2009:1496)

Journal article

Superhydrophobic and superhydrophilic plant surfaces: an inspiration for biomimetic materials

Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences | 16/03/2009 | K. Koch, W. Barthlott

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Reference

“…Although most studied functional changes were not directly associated with the transition from atmospheric to tank form, our results are consistent with the notion that the atmospheric stage is broadly associated with increased drought tolerance, whereas (larger) tanks allow improved access to nutrients.” (Zotz et al. 2004: 1350).

Journal article

Physiological and anatomical changes during the early ontogeny of the heteroblastic bromeliad, Vriesea sanguinolenta, do not concur with the morphological change from atmospheric to tank form

Plant, Cell & Environment | 22/11/2004 | G. ZOTZ, A. ENSLIN, W. HARTUNG, H. ZIEGLER

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