Red-leaved trees -- efficiency of generating nutrients

[ratatoskK]

Most trees have green leaves with chlorophyll for generating nutrients. What’s the story with red-leaved trees? They seem to thrive in the same type of environment. They don’t look sickly. So presumably they are just as able to convert sunlight into nutrients. So why do most trees have green leaves? Are red-leaved trees weaker in some way that is not apparent to the eye?

[Arkcon]

For plants on dry land, the chlorophylls (there are two different types, at least for terrestrial plants) are still there. This is a common experiment for high school students – paper chromatography. You can separate the various plant pigments to see there are several there – the bight red of Autumn leaves isn’t made in the fall, its there right now, masked by the chlorophyll. These other pigments also absorb light, and transfer some of the energy they got from light to the chlorophyll molecules. The red plants just have the relative amounts different.

Note: for seaweeds, all such bets are off, they may well lack chlorophyll and simply make do with other pigments

[ratatoskK]

But which chlorophyll is more or less efficient, and by how much?

[cmyk]

There’s more energy in the absorption of smaller wavelengths of light (blue, violet), and less in the longer wavelengths (red, orange).

Most leaves appear green, because they’re absorbing these colors for energy, and we see only the greenish wavelengths reflected back to our eyes.

I’m not a biologist, but I’m sure there might be reasons complicated, known and/or unknown as to why plants evolved for those two ends of the EM spectrum.

But with evolution/natural selection being the ultimate trial and error mechanism for life, it must have something to do with a plant’s common ancestor (and its common ancestor) and so on, as it happened to find a metabolic/biological mix of pigments that worked and flourished.

[DSeid]

Green is very abundant in natural light so a fair amount can be reflected off, with a large amount still being absorbed. This link claims that

Chlorophyll in an intact
leaf can also absorb green light much more effectively than the
chlorophyll absorption spectrum (chlorophyll extract in a
spectrophotometer) indicates. One reason is that although green light is
absorbed with low efficiency, it has many chances to be absorbed because
it is repeatedly reflected from cell to cell by the complex leaf geometry
so it has many chances to be absorbed.

This site posits that the branch that led to plants did less well with green only because of the competition in those early days:

it may have been because competing organisms were absorbing much of the green wavelengths billions of years ago, so algae (the earliest plants) reflected the green away and instead absorbed the red and blue hues that remained.

Early in Earth’s history, the oceans were dominated by archaea, bacteria-like organisms that are often purple in color, due to a pigment used to create energy from the sun in a process analogous to photosynthesis (but completely differently at the chemical level). As algae came along, they would have found a beneficial niche by utilizing the unused red and blue wavelengths (and reflecting the green). If you compare the absorption spectra of chlorophyll (plants) and retinal (the pigment in archaea), they are mirrors of each other, which supports this theory.

Why archaea never evolved into complex organisms like algae did into plants and trees is not known (to me, at least), but another roll of the evolutionary dice might have led to large, purple archaea-trees that could outcompete plants (since plants use only the weaker red/blue wavelengths)

So year round red leaves may have a slight competitive advantage by absorbing more green light if what they did was have more green absorbing chlorophyll But what seems to be the case for many at least is they just have less of the green reflecting chlorophyll leaving more of the load to be carried by carotenoids that absorb green but convert the light to energy less efficiently than chlorophyll does. Such is fine enough for a smaller tree in bright light anyway.

Any given plant that photosynthesizes contains chlorophyll-a, chlorophyll-b, carotenoids, etc.but in different proportions. Regular maple, lots of green; Japanese maple,not so much. There is so much chlorophyll in most plants that the green overpowers the other colors (reds and yellows) and you can’t see them. In the fall, the chlorophyll fades and leaves “turn” red or yellow or orange. Japanese maples do fine with what they have (notice most are dwarfs) as long as they are in the sun.
A bit of trivia - if you place a Japanese maple in the shade for a few days, its leaves will start turning green!

[TriPolar]

We have Red Maples all over the place around here. They’re not the ornamental type like Japanese Maples, the leaves are indistinquishable from other maples except for the color. They regularly change from red to green through the year. They have leaves earlier in the season than the other trees, and keep them later. They grow well with conjoined trunks, and one set I planted together has a tree with only green leaves. I don’t know if it’s a mutant, recessive gene, or cross pollination.

Anyway, there’s no indication these trees don’t grow at least as well as other species in the area. Extra red chlorophyll can’t be much of a problem in this climate.

[TriPolar]

ETA: Turns out the Red Maple is the state tree of Rhode Island.

[DSeid]

@TriPolar

… Extra red chlorophyll can’t be much of a problem in this climate.

A bit of a correction: plants do not have any red chlorophyll, they have other not-green pigments, such as carotenoids and flavanoids, that show up when there is less chlorophyll present. Red shows primarily with larger amounts of anthocyanin (according to that source).

Here’s an explanation of why those Red Maples do what they do:

Some species of trees, such as Maples, will form a red pigment in the fall if the days are warm and the nights cold. These trees produce sugar in the leaves during the day, but this sugar can’t move out when the nights are cold and the leaf’s connections to the tree begin to break down. The high sugar concentration favors the formation of a class of pigments called anthocyanins, which are red. So, the leaves left out in the sunlight turned red by this process.

[ratatoskK]

DSeid – For trees that have red leaves during the growing season (such as red maples), what makes the leaves red?

[Arkcon]

@ratatoskK

DSeid – For trees that have red leaves during the growing season (such as red maples), what makes the leaves red?

Anthocyanins is the general term for red pigments in terrestrial plants. Autumn leaf color - Wikipedia And it looks like I was wrong above, it appears its formed in Autumn in response to the breakdown of chlorophyll. That could mean the red-leafed varieties just have that happening all the time, instead of just in late summer. The article above gives theories on the reason why leaves change color, perhaps the same phenomena applies at all times to the red leafed varieties.

[Arkcon]

Look at this page: Plant Chromatography for Kids « The Kitchen Pantry Scientist its an experimental science page for kids. You can do that experiment, and you’ll see, the red-leafed Japanese maple leaves have some hidden green chlorophyll along with the red anthocyanin. The green ordinary maple leaf will have some yellow xanthophyll hidden by the green (but minimal red anthocyanin, it appears I was wrong above)

[TriPolar]

@DSeid

A bit of a correction: plants do not have any red chlorophyll, they have other not-green pigments, such as carotenoids and flavanoids, that show up when there is less chlorophyll present. Red shows primarily with larger amounts of anthocyanin (according to that source).

Here’s an explanation of why those Red Maples do what they do:

Yes, I should have said red leaved trees.

I took a close look at my green leafed variant. It’s leaves are identical in shape and size to the red leafed tree it has begun to conjoin with. The new branch shoots are red. I wonder what is producing this all green version. Can red maples cross pollinate with green leafed varieties and produce something like this?

The tall red maple the others sprung from is still a mix of green and red. It’s leaves usually come in mostly green in the spring, then become all red through the year.

[ratatoskK]

Just want to reiterate that I am talking about trees that have red leaves during the growing season. I know about leaves that are green during the season and why they turn red in the autumn.

If red-leaved and green-leaved trees are equally efficient then why are most trees green? If red is less efficient then why do they look so healthy?

[DSeid]

The deduction is that the same applies -

High amounts of anthocyanin and/or relatively low amounts of chlorophyll - which implies some beneficial effect of high levels of anthocyanins and/or adaptations for a very sunny environment.

In that regard a quick google finds this interesting article. High levels of anthocyanins seem to have some beneficial aspects:

1. Excess light can be harmful to a plant and there may be some role of anthocyanins as protection from excess light - “red leaf chloroplasts are exposed to less light because it is attenuated by anthocyanins, whereas green leaf chloroplasts are better equipped to dissipate excess light as heat. In addition to light attenuation, anthocyanins may participate in photoprotection through their anti oxidant capacity”

2. High levels of anthocyanins decrease damage from insect herbivores: “young red leaves of Q. coccifera are attacked less by insect consumers than young green leaves. We hypothesize that this is because anthocyanin accumulation masks the strong green reflectance that acts as an optical cue for consumers or increases the risk of consumer recognition by a predator, or both. Incidental attack may be a posteriori discouraged by the high phenolic investment of red leaves. … The reduced risk of insect attack probably compensates for the metabolic cost of chemical defense.”

FWIW.

[TriPolar]

@DSeid

2. High levels of anthocyanins decrease damage from insect herbivores: “young red leaves of Q. coccifera are attacked less by insect consumers than young green leaves. We hypothesize that this is because anthocyanin accumulation masks the strong green reflectance that acts as an optical cue for consumers or increases the risk of consumer recognition by a predator, or both. Incidental attack may be a posteriori discouraged by the high phenolic investment of red leaves. … The reduced risk of insect attack probably compensates for the metabolic cost of chemical defense.”

Defense mechanisms are pretty potent evolutionary adaptations.

From here:

The forest tent caterpillar is polyphagous but prefers to lay its eggs on particular trees. In the Northeast, the favored ovipositional hosts are sugar maple and red oak. However, the caterpillars frequently leave their natal tree and consume the leaves of many other species of hardwood trees. ** One exception is the red maple, which is not attacked by the caterpillars and is one of the few trees to remain foliated during outbreaks.**

(bolding mine)

[DSeid]

Great find! Cool.

[ratatoskK]

Where did red-leaved trees evolve? Did they all evolve in the same geographic area or in the same ecological conditions? Did they all evolve in a place where there are a lot of leaf-eating caterpillars? Are there areas where most trees have red leaves?

[TriPolar]

@ratatoskK

Where did red-leaved trees evolve? Did they all evolve in the same geographic area or in the same ecological conditions? Did they all evolve in a place where there are a lot of leaf-eating caterpillars? Are there areas where most trees have red leaves?

This article has some information. It’s something that may not be known yet. The red pigments that many trees have, or develop in the fall, may have been an adaptation to protect against insect damage, so the development of year round red leaves may not have been that big of a leap. The red maples are not as large as many other hardwood trees, and if not for insect infestations that take out the other trees the red maples may not have been so successful.