Why do most plants reflect green and others other colors?

Why do most plants reflect green and others other colors?

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I have read that chlorophyll absorbs red and blue.

As shown in detail in the absorption spectra, chlorophyll absorbs light in the red (long wavelength) and the blue (short wavelength) regions of the visible light spectrum. Green light is not absorbed but reflected, making the plant appear green. Chlorophyll is found in the chloroplasts of plants.

It did not mention what the difference in chlorophyll between a red leafed plant and a green plant?

Does chlorophyll only come in green? So what in chlorophyll determines if other colors than green are reflected in plants that are naturally red? If chlorophyll needed can only be green would not the color green and the red from a " pigment" look brown?

Japanese Blood Grass

Blue Selaginella

Solenostemon scutellarioides

Tl;dr : Some plants reflect green while others don't simply because some plants are green while others are not.

Plants contain chlorophyll, but are not 100% made of it. Parts of the plant that contain a high amount of chlorophyll will look green, (Leaves, stem) while other parts that contain less chlorophyll and contain more of other pigments will look different. The flower looks red because it contains a lot more red pigment than any other pigments. The fruit looks yellow because it contains a lot more yellow than other pigments. Carotene(orange) and Xanthophylls(yellow) are examples for pigments which absorb all colors except orange and yellow respectively, they reflect these colors. so it appears to be orange or yellow.

"Chlorophyll absorbs red and blue" is just another way of saying chlorophyll is green in colour.

All photosynthetic plants contain chlorophyll, and chlorophyll is green (leaving out various algae). Plant leaves often contain other pigments, which can mask the chlorophyll's green, or be masked by it.

A common example of the latter is the color of autumn leaves. The leaves contain various pigments such as xanthophylls, anthocyanins, and carotenoids that are generally masked by the green of the chlorophyll. As the trees prepare to drop their leaves in the fall, the chlorophyll decomposes, allowing the other pigments to become visible. Exactly what purpose(s) these other pigments serve isn't entirely clear. Some are thought to make photosynthesis more efficient, others might have functions where the color is irrelevant. See e.g.

Some plants may have a larger than average amount of other pigments, somewhat masking the chlorophyll's green, and giving rise to different shades of leaf color. Human selective breeding can increase these differences, giving rise to e.g. the purple-leaf plum or the almost golden color of some honey locusts:

Other plants, like the coleus, may have chloroplasts only in certain zones of the leaf, allowing other color combinations, which can be wildly amplified by human breeding:

Sometimes the colors can be structural, as with the Blue Selaginella pictured in the question, or the grayish colors of desert plants that are produced by protective hairs:

Finally, there are plants that don't have chlorophyll at all, but these don't photosynthesize. An example (common to the mountains hereabouts) is the brilliant red snow plant:… But it doesn't use the red pigment to photosynthesize, having become parasitic on soil fungi.

Why are plants green?

When sunlight shining on a leaf changes rapidly, plants must protect themselves from the ensuing sudden surges of solar energy. To cope with these changes, photosynthetic organisms -- from plants to bacteria -- have developed numerous tactics. Scientists have been unable, however, to identify the underlying design principle.

An international team of scientists, led by physicist Nathaniel M. Gabor at the University of California, Riverside, has now constructed a model that reproduces a general feature of photosynthetic light harvesting, observed across many photosynthetic organisms.

Light harvesting is the collection of solar energy by protein-bound chlorophyll molecules. In photosynthesis -- the process by which green plants and some other organisms use sunlight to synthesize foods from carbon dioxide and water -- light energy harvesting begins with sunlight absorption.

The researchers' model borrows ideas from the science of complex networks, a field of study that explores efficient operation in cellphone networks, brains, and the power grid. The model describes a simple network that is able to input light of two different colors, yet output a steady rate of solar power. This unusual choice of only two inputs has remarkable consequences.

"Our model shows that by absorbing only very specific colors of light, photosynthetic organisms may automatically protect themselves against sudden changes -- or 'noise' -- in solar energy, resulting in remarkably efficient power conversion," said Gabor, an associate professor of physics and astronomy, who led the study appearing today in the journal Science. "Green plants appear green and purple bacteria appear purple because only specific regions of the spectrum from which they absorb are suited for protection against rapidly changing solar energy."

Gabor first began thinking about photosynthesis research more than a decade ago, when he was a doctoral student at Cornell University. He wondered why plants rejected green light, the most intense solar light. Over the years, he worked with physicists and biologists worldwide to learn more about statistical methods and the quantum biology of photosynthesis.

Richard Cogdell, a botanist at the University of Glasgow in the United Kingdom and a coauthor on the research paper, encouraged Gabor to extend the model to include a wider range of photosynthetic organisms that grow in environments where the incident solar spectrum is very different.

"Excitingly, we were then able to show that the model worked in other photosynthetic organisms besides green plants, and that the model identified a general and fundamental property of photosynthetic light harvesting," he said. "Our study shows how, by choosing where you absorb solar energy in relation to the incident solar spectrum, you can minimize the noise on the output -- information that can be used to enhance the performance of solar cells."

Coauthor Rienk van Grondelle, an influential experimental physicist at Vrije Universiteit Amsterdam in the Netherlands who works on the primary physical processes of photosynthesis, said the team found the absorption spectra of certain photosynthetic systems select certain spectral excitation regions that cancel the noise and maximize the energy stored.

"This very simple design principle could also be applied in the design of human-made solar cells," said van Grondelle, who has vast experience with photosynthetic light harvesting.

Gabor explained that plants and other photosynthetic organisms have a wide variety of tactics to prevent damage due to overexposure to the sun, ranging from molecular mechanisms of energy release to physical movement of the leaf to track the sun. Plants have even developed effective protection against UV light, just as in sunscreen.

"In the complex process of photosynthesis, it is clear that protecting the organism from overexposure is the driving factor in successful energy production, and this is the inspiration we used to develop our model," he said. "Our model incorporates relatively simple physics, yet it is consistent with a vast set of observations in biology. This is remarkably rare. If our model holds up to continued experiments, we may find even more agreement between theory and observations, giving rich insight into the inner workings of nature."

To construct the model, Gabor and his colleagues applied straightforward physics of networks to the complex details of biology, and were able to make clear, quantitative, and generic statements about highly diverse photosynthetic organisms.

"Our model is the first hypothesis-driven explanation for why plants are green, and we give a roadmap to test the model through more detailed experiments," Gabor said.

Photosynthesis may be thought of as a kitchen sink, Gabor added, where a faucet flows water in and a drain allows the water to flow out. If the flow into the sink is much bigger than the outward flow, the sink overflows and the water spills all over the floor.

"In photosynthesis, if the flow of solar power into the light harvesting network is significantly larger than the flow out, the photosynthetic network must adapt to reduce the sudden over-flow of energy," he said. "When the network fails to manage these fluctuations, the organism attempts to expel the extra energy. In doing so, the organism undergoes oxidative stress, which damages cells."

The researchers were surprised by how general and simple their model is.

"Nature will always surprise you," Gabor said. "Something that seems so complicated and complex might operate based on a few basic rules. We applied the model to organisms in different photosynthetic niches and continue to reproduce accurate absorption spectra. In biology, there are exceptions to every rule, so much so that finding a rule is usually very difficult. Surprisingly, we seem to have found one of the rules of photosynthetic life."

Gabor noted that over the last several decades, photosynthesis research has focused mainly on the structure and function of the microscopic components of the photosynthetic process.

"Biologists know well that biological systems are not generally finely tuned given the fact that organisms have little control over their external conditions," he said. "This contradiction has so far been unaddressed because no model exists that connects microscopic processes with macroscopic properties. Our work represents the first quantitative physical model that tackles this contradiction."

Next, supported by several recent grants, the researchers will design a novel microscopy technique to test their ideas and advance the technology of photo-biology experiments using quantum optics tools.

"There's a lot out there to understand about nature, and it only looks more beautiful as we unravel its mysteries," Gabor said.

How plants use light

Photosynthesis is essentially the process of the plant converting atmospheric gas carbon dioxide (CO2) and water (H2O) into simple sugars, producing oxygen (O2) as a by-product. To do this, it needs energy and it gets that energy from the light it absorbs.

By absorbing light, the object also absorbs some of the energy carried by the light. In the case of plants, it is the pigment chlorophyll which absorbs the light, and it is picky about which wavelengths it absorbs – mostly opting for red light, and some blue light.

The absorbed energy causes the electrons in the object to become excited.

When electrons are excited, they are promoted from a level of low energy to a level of higher energy. The energy in the light makes the electrons excited and removes energy from the light – this is an example of the first law of thermodynamics – energy is neither created nor destroyed it can only be transferred or changed from one form to another.

That process takes place in specific compartments within cells called chloroplasts and is split into two stages

  1. 1 – The first stage sees a sequence of reactions which are ‘light-dependent’. Chloroplasts contain many discs called thylakoids, which are packed with chlorophyll. Structures within the thylakoids known as photosystems form the core machinery of photosynthesis and at the centre of each photosystem are a ‘special pair’ of chlorophyll molecules. Electrons in these chlorophyll molecules are excited upon absorption of sunlight. The job of the rest of the chlorophyll molecules in the chloroplast is simply to pass energy towards the special pair
  2. 2 – A second set of reactions are light-independent. These use the energy captured during the light-dependent step to make sugars. These reactions occur in the fluid which bathes the thylakoids (the stroma)

During these reactions, CO2 dissolves in the stroma and is used in the light-independent reactions. This gas is used in a series of reactions which results in the production of sugars. Sugar molecules are then used by the plant as food in a similar way to humans, with excess sugars stored as starch, ready to be used later, much like fat storage in mammals.

Therefore, the red end of the light spectrum excites the electrons in the leaves of the plants, and the light reflected (or unused) is made up of more of wavelengths of the complementary (or opposite) colour, green.

So, plants and their leaves look green because the “special pair” of chlorophyll molecules uses the red end of the visible light spectrum to power reactions inside each cell. The unused green light is reflected from the leaf and we see that light. The chemical reactions of photosynthesis turn carbon dioxide from the air into sugars to feed the plant, and as a by-product the plant produces oxygen.

It is this preference for light at the red end of the spectrum that is behind Dr Brande Wulff and his team’s development of speed breeding technology. The technique first used by NASA to grow crops in space uses extended day-length, enhanced LED lighting and controlled temperatures to promote rapid growth of crops.

It speeds up the breeding cycle of plants: for example, six generations of wheat can be grown per year, compared to two generations using traditional breeding methods.

By shortening breeding cycles, the method allows scientists and plant breeders to fast-track genetic improvements such as yield gain, disease resistance and climate resilience in a range of crops such as wheat, barley, oilseed rape and pea.”

Apart from coloring, has chlorophyll any other role?

The green color of chlorophyll is secondary to its importance in nature as one of the most fundamentally useful chelates. It channels the energy of sunlight into chemical energy, converting it through the process of photosynthesis. In photosynthesis, chlorophyll absorbs energy to transform carbon dioxide and water into carbohydrates and oxygen. This is the process that converts solar energy to a form that can be utilized by plants, and by the animals that eat them, to form the foundation of the food chain.

Chlorophyll is a molecule that traps light - and is called a photoreceptor.

How Color Vision Came to the Animals

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Daniel Hernanz Ramos/Getty Images

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Animals are living color. Wasps buzz with painted warnings. Birds shimmer their iridescent desires. Fish hide from predators with body colors that dapple like light across a rippling pond. And all this color on all these creatures happened because other creatures could see it.

The natural world is so showy, it’s no wonder scientists have been fascinated with animal color for centuries. Even today, the questions how animals see, create, and use color are among the most compelling in biology.

Until the last few years, they were also at least partially unanswerable—because color researchers are only human, which means they can’t see the rich, vivid colors that other animals do. But now new technologies, like portable hyperspectral scanners and cameras small enough to fit on a bird’s head, are helping biologists see the unseen. And as described in a new Science paper, it's a whole new world.

The basics: Photons strike a surface—a rock, a plant, another animal—and that surface absorbs some photons, reflects others, refracts still others, all according to the molecular arrangement of pigments and structures. Some of those photons find their way into an animal’s eye, where specialized cells transmit the signals of those photons to the animal’s brain, which decodes them as colors and shapes.

It's the brain that determines whether the colorful thing is a distinct and interesting form, different from the photons from the trees, sand, sky, lake, and so on it received at the same time. If it’s successful, it has to decide whether this colorful thing is food, a potential mate, or maybe a predator. “The biology of color is all about these complex cascades of events,” says Richard Prum, an ornithologist at Yale University and co-author of the paper.

In the beginning, there was light and there was dark. That is, basic greyscale vision most likely evolved first, because animals that could anticipate the dawn or skitter away from a shadow are animals that live to breed. And the first eye-like structures—flat patches of photosensitive cells—probably didn't resolve much more than that. It wasn't enough. “The problem with using just light and dark is that the information is quite noisy, and one problem that comes up is determining where one object stops and another one starts. ” says Innes Cuthill, a behavioral ecologist at the University of Bristol and coauthor of the new review.

Color adds context. And context on a scene is an evolutionary advantage. So, just like with smart phones, better resolution and brighter colors became competitive enterprises. For the resolution bit, the patch light-sensing cells evolved over millions of years into a proper eye—first by recessing into a cup, then a cavity, and eventually a fluid-filled spheroid capped with a lens. For color, look deeper at those light-sensing cells. Wedged into their surfaces are proteins called opsins. Every time they get hit with a photon—a quantum piece of light itself—they transduce that signal into an electrical zap to the rudimentary animal's rudimentary brain. The original light/dark opsin mutated into spin-offs that could detect specific ranges of wavelengths. Color vision was so important that it evolved independently multiple times in the animal kingdom—in mollusks, arthropods, and vertebrates.

In fact, primitive fish had four different opsins, to sense four spectra—red, green, blue, and ultraviolet light. That four-fold ability is called tetrachromacy, and the dinosaurs probably had it. Since they're the ancestors of today’s birds, many of them are tetrachromats, too.

But modern mammals don't see things that way. That's probably because early mammals were small, nocturnal things that spent their first 100 million years running around in the dark, trying to keep from being eaten by tetrachromatic dinosaurs. “During that period the complicated visual system they inherited from their ancestors degraded,” says Prum. “We have a clumsy, retrofitted version of color vision. Fishes, and birds, and many lizards see a much richer world than we do."

In fact, most monkeys and apes are dichromats, and see the world as greyish and slightly red-hued. Scientists believe that early primates regained three-color vision because spotting fresh fruit and immature leaves led to a more nutritious diet. But no matter how much you enjoy springtime of fall colors, the wildly varicolored world we humans live in now isn't putting on a show for us. It's mostly for bugs and birds. “Flowering plants of course have evolved to signal pollinators,” says Prum. “The fact that we find them beautiful is incidental, and the fact that we can see them at all is because of an overlap in the spectrums insects and birds can see and the ones we can see.”

And as animals gained the ability to sense color, evolution kickstarted an arms race in displays—hues and patterns that aided in survival became signifiers of ace baby-making skills. Almost every expression of color in the natural world came about to signal, or obscure, a creature to something else.

For instance, "aposematism" is color used as a warning—the butterfly’s bright colors say “don’t eat me, you'll get sick.” "Crypsis" is color used as camouflage. Color serves social purposes, too. Like, in mating. Did you know that female lions prefer brunets? Or that paper wasps can recognize each others’ faces? “Some wasps even have little black spots that act like karate belts, telling other wasps not to try and fight them,” says Elizabeth Tibbetts, an entomologist at the University of Michigan.

But animals display colors using two very different methods. The first is with pigments, colored substances created by cells called chromatophores (in reptiles, fish, and cephalopods), and melanocytes (in mammals and birds). They absorb most wavelengths of light and reflect just a few, limiting both their range and brilliance. For instance, most animals cannot naturally produce red they synthesize it from plant chemicals called carotenoids.

The other way animals make color is with nanoscale structures. Insects, and, to a lesser degree, birds, are the masters of color-based structure. And compared to pigment, structure is fabulous. Structural coloration scatters light into vibrant, shimmering colors, like the shimmering iridescent bib on a Broad-tailed hummingbird, or the metallic carapace of a Golden scarab beetle. And scientists aren't quite sure why iridescence evolved. Probably to signal mates, but still: Why?

The question of iridescence is similar to most questions scientists have about animal coloration. They understand what the colors do in broad strokes, but there's till a lot of nuance to tease out. This is mostly because, until recently, they were limited to seeing the natural world through human eyes. “If you ask the question, what’s this color for, you should approach it the way animals see those colors,” says Tim Caro, a wildlife biologist at UC Davis and the organizing force behind the new paper. (Speaking of mysteries, Caro recently figured out why zebras have stripes.)

Take the peacock. “The male’s tail is beautiful, and it evolved to impress the female. But the female may be impressed in a different way than you or I,” Caro says. Humans tend to gaze at the shimmering eyes at the tip of each tail feather peahens typically look at the base of the feathers, where they attach to the peacock’s rump. Why does the peahen find the base of the feathers sexy? No one knows. But until scientists strapped to the birds' heads tiny cameras spun off from the mobile phone industry, they couldn't even track the peahens' gaze.

Another new tech: Advanced nanomaterials give scientists the ability to recreate the structures animals use to bend light into iridescent displays. By recreating those structures, scientists can figure out how genetically expensive they are to make.

Likewise, new magnification techniques have allowed scientists to look into an animal’s eye structure. You might have read about how mantis shrimp have not three or four but a whopping 12 different color receptors, and how they see the world in psychedelic hyperspectral saturation. This isn’t quite true. Those color channels aren’t linked together—not like they are in other animals. The shrimp probably aren’t seeing 12 different, overlapping color spectra. “We are thinking maybe those color receptors are being turned on or off by some other, non-color, signal,” says Caro.

But perhaps the most important modern innovation in biological color research is getting all the different people from different disciplines together. “There are a lot of different sorts of people working on color,” says Caro. “Some behavioral biologists, some neurophysiologists, some anthropologists, some structural biologists, and so on.”

And these scientists are scattered all over the globe. He says the reason he brought everyone to Berlin is so they could finally synthesize all these sub-disciplines together, and move into a broader understanding of color in the world. The most important technology in understanding animal color vision isn't a camera or a nanotech surface. It's an airplane. Or the internet.

Green light: Is it important for plant growth?

Green light is considered the least efficient wavelength in the visible spectrum for photosynthesis, but it is still useful in photosynthesis and regulates plant architecture.

Sometimes one may hear that plants don&rsquot use green light for photosynthesis, they reflect it. However, this is only partly true. While most plants reflect more green than any other in the visible spectrum, a relatively small percentage of green light is transmitted through or reflected by the leaves. The majority of green light is useful in photosynthesis. The relative quantum efficiency curve (Photo 1) shows how efficiently plants use wavelengths between 300 and 800 nm. Green light is the least efficiently used color of light in the visible spectrum.

Photo 1. Relative quantum efficiency curve. (Adapted by Erik Runkle from McCree, 1972. Agric. Meteorology 9:191-216.)

As a part of a series of experiments performed in enclosed environments, Michigan State University Extension investigated how different wavebands of light (blue, green and red) from LEDs influenced growth of seedlings. We grew tomato &lsquoEarly Girl,&rsquo salvia &lsquoVista Red,&rsquo petunia &lsquoWave Pink,&rsquo and impatiens &lsquoSuperElfin XP Red&rsquo in growth chambers for four to five weeks at 68 degrees Fahrenheit under 160 µmol∙m -2 ∙s -1 of LED or fluorescent light. The percentages from each LED color were: B25+G25+R50 (25 percent of light from blue and green LEDs and 50 percent from red LEDs) B50+G50 B50+R50 G50+R50 R100 and B100.

Plants grown with 50 percent green and 50 percent red light were approximately 25 percent shorter than those grown under only red light, but approximately 50 percent taller than all plants grown under more than 25 percent blue light (Photo 2). Therefore, blue light suppressed extension growth more than green light in an enclosed environment. Twenty-five percent green light could substitute for the same percentage of blue light without affecting fresh weight. However, the electrical efficiency of the green LEDs was much lower than that of blue LEDs. To read more about this experiment, please read &ldquoGrowing Plants under LEDs: Part Two&rdquo in Greenhouse Grower.

Photo 2. Salvia grown for four weeks under the same intensity of blue (B), green (G) and red (R) LEDs or fluorescent lamps (FL). The number after each color represents the percentage of that color, e.g., B50+R50 means that plants were grown under 50 percent blue light and 50 percent red light.

One potential advantage of including green in a light spectrum is to reduce eye strain of employees. Under monochromatic, or sometimes two colors of light such as blue and red, plants may not appear their typical color, which could make noticing nutritional, disease or insect pest issues difficult. Another potential advantage of green light is that it can penetrate a canopy better than other wavebands of light. It&rsquos possible that with better canopy penetration, lower leaves will continue to photosynthesize, leading to less loss of the lower leaves.

Green Is Calming

Shades of green found in nature may help put us at ease in a new place. For this reason, designers often feature the color green in public spaces like restaurants and hotels.

One study found a "green exercise effect" on participants who exercised indoors while watching a video of outdoor space with a green-colored overlay.

They experienced less mood disturbance and less perceived exertion compared to when they watched the same video with a red overlay or a gray overlay.

Why Are Leaves Green?

Leaves appear green because of the chlorophyll they contain. Chlorophyll is the part of the leaf that uses carbon dioxide, sunlight and water to produce sugar. A leaf with plenty of chlorophyll masks other pigment colors.

A pigment is a substance that absorbs, reflects and transmits visible light, which consists of colors that the human eye can see. When white light illuminates a pigment, the color that a person sees on leaves is the color of light that the pigment reflects and/or transmits. The pigment absorbs the rest of the colors of light.

Chlorophyll is a green pigment found in the chloroplasts of plants, and it is an essential component of photosynthesis. Leaves often show a vivid green color when they are close to other leaves. This happens because the light people see bounces off the green leaves before it reaches the eyes. Chlorophyll utilizes mostly red and blue light energy, while the green energy passes through or bounces off the leaves and reaches a person&rsquos eyes. Leaves then appear green. As autumn comes to an end, plants and trees produce less chlorophyll because light regulates the production of chlorophyll. Chlorophyll has a constant decomposition rate, and the green hue begins to fade when chlorophyll starts to decompose. Other pigments that affect leaf color are anthocyanin pigments that cause leaves to look red and carotenoids that cause leaves to appear red, yellow or orange.

Why Is the Ocean Different Colors in Different Places?

Someone gazing out at the ocean from the Maine coast sees very different hues than someone squinting at the sea from a sunny beach on a Greek island. So why does the ocean come in so many shades of blue?

First of all, as NASA oceanographer Gene Carl Feldman points out, "The water of the ocean is not blue, it's clear. The color of the ocean surface for the most part is based on depth, what's in it and what's below it."

A glass of water will, of course, appear clear as visible light passes through it with little to no obstruction. But if a body of water is deep enough that light isn't reflected off the bottom, it appears blue. Basic physics explains why: Light from the sun is made up of a spectrum of different wavelengths. The longer wavelengths appear to our eyes as the reds and oranges, while the shorter ones appear blue and green. When the sun's light strikes the ocean, it interacts with water molecules and can be absorbed or scattered. If nothing is in the water except water molecules, light of shorter wavelengths is more likely to hit something and scatter, making the ocean appear blue. The longer, red portions of sunlight, meanwhile, are absorbed near the surface.

Depth and the ocean bottom also influence whether the surface appears a dusky dark blue, as in parts of the Atlantic, or casts a sapphire-like shimmer as in tropical locations. "In Greece, the water is this beautiful turquoise color because the bottom is either white sand or white rocks," Feldman explains. "What happens is the light comes down and blue light gets down, hits the bottom and then reflects back up so you make this beautiful light blue color in the water."

Color Reflects Ocean Health

And then there's the fact that the ocean is rarely clear, but is instead teeming with tiny plant and animal life or filled with suspended sediment or contaminants. Oceanographers monitor the ocean's color as doctors read the vital signs of their patients. Color seen on the ocean's surface reflect what's going on in its vast depths.

Feldman, who's based at the NASA Goddard Space Flight Center in Maryland, studies images taken by the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) satellite, launched in 1997. From its perch, more than 400 miles (644 kilometers) above Earth, the satellite captures Van Gogh-like swirls of the ocean's colors. The patterns are not only mesmerizing, but they also reflect where sediment and runoff may make water appear a dull brown color and where microscopic plants, called phytoplankton, collect in nutrient-rich waters, often tinting it green.

Phytoplankton use chlorophyll to capture energy from the sun to convert water and carbon dioxide into the organic compounds. Through this process, called photosynthesis, phytoplankton generate about half of the oxygen we breathe. While most phytoplankton give ocean water a green tint, some lend it a yellow, reddish or brown tint, Feldman says.

Oceans with high concentrations of phytoplankton can appear blue-green to green, depending on the density. Greenish water may not sound appealing, but as Feldman says, "If it weren't for phytoplankton we wouldn't be here." Phytoplankton serve as the base of the food web and primary source of food for zooplankton, which are tiny animals eaten by fish. The fish are then eaten by bigger animals like whales and sharks.

It's when oceans become polluted with runoff that the amount of phytoplankton can escalate to unhealthy levels. Phytoplankton feed on the pollutants, flourish and die, sinking to the bottom to decompose in a process that depletes oxygen from the water.

The Climate Change Effect

Over the past 50 years, ocean zones with depleted oxygen have more than quadrupled to an area roughly the size of the European Union, or 1,728,099 square miles (4,475,755 square kilometers), according to a study published in January 2018 in the journal Science. Part of the cause may be an increase in ocean temperature due to climate change since warmer water supports less oxygen. In coastal areas, phytoplankton blooms are suspected to be the cause. Phytoplankton may serve as the base of the ocean food chain, but as Feldman says, "Too much of a good thing is not a good thing."

On a map on Feldman's office wall is a marker showing where there is little human interference and ocean water is perhaps the clearest on the planet. In this region, off the coast of Easter Island in the southeast Pacific Ocean, the water is deep and remarkably clear due to its location in the middle of a giant oceanic gyre, or large circular current. Its central location means there is minimal mixing of ocean layers and nutrients aren't pushed up from the deep bottom. The purity of the water here, coupled with its depth make the ocean here appear a deeper indigo than perhaps anywhere else.

"The light just keeps going down, down, down there's nothing that bounces it back," Feldman says, "Here is the deepest blue you'll ever see."

A species of bacteria called Synechococcus cyanobacteria has the ability to adjust its color to match different wavelengths of light across the world's oceans. These bacteria harness light to capture carbon dioxide from the air and produce energy. As research published Feb. 12, 2018 in the Proceedings of the National Academy of Sciences showed, the bacteria contain genes that lend them the chameleon-like ability to alter their color in order to survive in waters of any color and to maximize their ability to process the ambient light around them.

12 Answers 12

Yes, the colour will block some light, but not too much. The only reason they sell these green plastic coverings on a frame is because they're thought to be more aesthetically pleasing than looking at clear plastic, and because the material they're made from is somewhat tougher than clear plastic.

I received an answer from an OGrow representative. OGrow is a manufacturer of greenhouses.

Can we get an official response on how to choose between the green and clear coverings? I'm mainly going to grow fruit trees and shrubs. Would fruit trees do better with the clear covering because bit provides full sun?

While we cannot determine which is better for the particular kind tree you are planting, we can advise you with some of the pros and cons regarding the Clear/PVC vs. PE greenhouse cover.

PVC: The plastic used on our clear covers generate extra heat and is better for cold climate area. Plants can be seen to add beauty to your garden!

PE: Customers and greenhouse experts prefer PE over PVC claiming that the PVC material contains a toxic load that can be damaging to sensitive plants. The PE material is made out of stronger elements, and protects from sun, for plants that do better with less exposure to the sun.

Good luck!

Wow! I had no idea that the clear covering could be poisonous. I guess that's why plastics smell bad when they're baking out in the sun. What fruit trees would benefit from shade though?

Several of the answers here are incorrect. Green plastic absorbs green light or reflects it which is why it appears green. Green is chosen because if you want to reduce the light intensity to the inside of the greenhouse, you use green because it's not used by the plants to any significant degree. The filtering is not perfect which is why you might still see some green on the other side of the plastic, or it could be that some white light is being reflected off another surface onto the plastic.

I have a little plastic greenhouse but the green is just green stripes running through clear plastic. However, at a distance, it looks green, and the same as in the image posted with the question.

Green filters, such as the green colored plastic, allows more green light than other wavelengths to pass through. For plants, the blue and red part of the spectrum are the most important. Since plant leaves are generally green, they reflect green light. I don't think the green color would be the best choice to grow plants under.

Red would probably be better. Some people like to use red colored plastic to cover the soil before planting tomatoes and claim that it helps improve yield.

Regarding the email you received. Plastic doesn't "generate" heat. It partially blocks light and heat and also helps retain it by not allowing cold air to enter and warmer air to leave.

All (most?) plastics leach some of their chemicals when in contact with water. Polyethelene may leach less or different substances I forget which but high density polyethelene (HDPE) I hear leaches less.

From what I hear those small greenhouses may not have UV stabilized plastic sheeting which means they will degrade faster under the sun's radiation. Maybe only lasting one season.

There are specific plastic films made to be used for outdoor greenhouses. I used one for my raised bed cover for the square foot gardening box I built last year. It's a UV stabilized low density polyethelene. I believe since it breaks down slower it won't leach as much of it's chemicals as fast.

Green filters, such as the green colored plastic, allows more green light than other wavelengths to pass through. For plants, the blue and red part of the spectrum are the most important. Since plant leaves are generally green, they reflect green light. I don't think the green color would be the best choice to grow plants under.

I'm pretty sure a green filter would block the green spectrum allowing the plants to absorb more of the others. The color you are seeing is the range of spectrum that ISN'T being absorbed. So if you think about it..if the material is is reflecting the green less green light.

While looking for an answer to this question myself, I came across this article which talks about actual studies that have been done regarding the colour of plastic greenhouse covers. In particular it states:

In studies, it has been found that using green plastic to cover a greenhouse results in plants which are slightly (but very slightly) shorter than plants grown in a greenhouse with a clear plastic covering. There isn’t all that much green in sunlight, it seems, since overall, green plastic lets in almost the same amount of light overall. It’s probably not preferable to clear plastic as a greenhouse covering, but if you find yourself in the unlikely situation of having only green plastic sheeting available for your greenhouse, it will do if need be.

There are other questions to ask. Where are these Green covers coming from and which market were they designed for? Perhaps for example these green plastic greenhouses were made in China. Now since China is relatively close to Australia and has a strong trading relationship with them perhaps it's possible that they were designed for the Australian market. The sunlight in an Australian summer could be too powerful for many plants to survive. Perhaps this is why the concept of a green greenhouse has come about? Green obviously filters out much of the red and blue needed by plants, (more of the blue spectrum in early development and more of the red spectrum later on during flowering). Or perhaps Green just works out cheaper for the manufacturer. Generally green is more UV resistant so perhaps it is simply for longevity.

You are not likely to find a clear PVC cover (as in the OP second photo) that will survive sunlight for more than one season. The green one (as in the OP first photo) looks like a polyethylene mesh which is often treated to resist UV radiation, which means you should get two or more years out of it.
If treated, the green one will last at least twice as long as the other which should be a major purchasing consideration.

Chinese-made greenhouses use green plastic to communicate to uneducated consumers that they are greenhouses. It is mostly a marketing tool by people who don't know physics. Green filters do not block out green. On the contrary, they partially filter out the other colors, like red, which plants need. This is why plants emit green light, which they can't use. The Chinese suits making these atrocities should read my post and consider using red hues in their plastic coverings.

p.s. A more important question is the IR transmission vs. optical transmission coefficients, which if tweaked carefully can increase the winter air temperature of a greenhouse, another important variable.

Caveat: This answer assumes that the green plastic shown is pigmented green and thus transmits green light into the greenhouse. Certain metal coatings could reflect green light but transmit blue and red wavelengths (which would provide plants with an optimal environment but be rather expensive to engineer). To understand the illogic of green pigmented plastic, take a look at the absorption efficiency of plant pigments . The solid line, Clorophyll a, is the most important pigment for most of the terrestrial plants. The two peaks around 430 and 660 nm mean plants most efficiently convert blue and red light into energy for growth and respiration. PAR (photosynthetically active radiation) light meters are calibrated to measure blue and red light. Unfortunately, green-pigmented plastic is green because it absorbs about 50% of the PAR radiation. Green greenhouses may sell because they look nice, and still transmit about half of the PAR radiation, but a 50% shade cloth would produce far more cooling inside the greenhouse without reducing PAR one bit more. I've got a friend who just bought a green plastic greenhouse, and I am going to offer to help him replace it with a proper 6-mil UVA shielded greenhouse film. And see if we can get his tomatoes and peppers growing properly.

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