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From this chart it appears that the star types closest to our own are K-type (oranger, a little cooler, and less than half as bright) and F-type (bluer, a little warmer, and much brighter). If I want to place an "earth-like" planet around one of these star types, how should I expect plant life on my planet to develop differently compared to Earth?

By "earth-like" I mean a planet that has temperature, terrain, water, and atmosphere conducive to the development of higher life forms (eventually sentient ones). How does the star type affect the appearance, growth, types, density, etc of plants? Should one star type lead to denser (or sparser) jungles, taller (or shorter) trees, different kinds of fruits, etc?

I think this question is related. I don't know enough chemistry to say how related, though.

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  • $\begingroup$ Yes, that question is related. Chlorophyll works in one way - if you have a different chemical (a type of non-chlorophyll) doing energy capture it will work another way, with (perhaps) different portions of the spectrum, which different stars may (or may not) produce in different abundances. $\endgroup$ – user3082 Mar 9 '15 at 12:35
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    $\begingroup$ As a side note more recently formed stars should have accretionary discs with higher heavy metal content so any worlds that form will be higher in substances that life as we know it finds pretty toxic. This could be quite important in defining available development pathways since there are certain substances, like Arsenic, that are relatively rare on Earth, that are toxic to all known Carbon-based life-structures. $\endgroup$ – Ash Jun 19 '18 at 17:27
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Let's think about this in terms of peak emission. Wien's displacement law tells us that the peak emission wavelength of a black body, $\lambda_{\text{max}}$, is inversely proportional to its temperature, $T$: $$\lambda_{\text{max}}=\frac{b}{T}$$ where $b$ is Wien's displacement constant; $b\simeq2.9\times10^{-3}\text{ m K}$. Using this and some assumptions about temperature, we can determine the peak of a star's spectrum, given that most stars are well-approximated as black bodies. Here, we assume that $T$ is the star's effective temperature, and pick a temperature in the general range of each type. I'm going to use the Harvard spectral classification. $$\begin{array}{|c|c|c|c|} \hline \text{Star type} & \text{Color} & T (\text{K}) & \lambda_{\text{max}}(\text{nm})\\ \hline \text{O} & \text{blue} & 35,000 & 82.9\\ \hline \text{B} & \text{blue-white} & 20,000 & 145\\ \hline \text{A} & \text{white} & 8,000 & 363\\ \hline \text{F} & \text{yellow-white} & 7,000 & 414\\ \hline \text{G} & \text{yellow} & 5,500 & 527\\ \hline \text{K} & \text{orange} & 4,000 & 725\\ \hline \text{M} & \text{red} & 3,000 & 967\\ \hline \end{array}$$ Next, we have to assume that the plants are somewhat like the ones found on Earth - they use the same compounds and processes to survive. Life on Earth is all that currently exists in our dataset, and it's all we have to work with before delving into too much speculation.

One important process is photosynthesis. There are a variety of photosynthetic pigments available. I was able to find a book chapter detailing many of them along with their key property here, the wavelength(s) of maximum absorption $\lambda_{\text{abs}}$. Here's a table of the relevant ones: $$\begin{array}{|c|c|c|} \hline \text{Pigment} & \lambda_{\text{abs}}(\text{nm}) & \text{Occurrence}\\ \hline \text{Chlorophyll a} & 435, 670\text{-6}80 & \text{Photosynthetic plants}\\ \hline \text{Chlorophyll b} & 480, 650 & \text{Higher plants; green algae}\\ \hline \text{Chlorophyll c} & 435, 645 & \text{Diatoms; brown algae}\\ \hline \text{Chlorophyll d} & 435, 740 & \text{Red algae}\\ \hline \text{Chlorobium chlorophyll} & 750, 760 & \text{Green bacteria}\\ \hline \text{Bacteriochlorophyll a} & 800, 850, 890 & \text{Purple bacteria; green bacteria}\\ \hline \text{Bacteriochlorophyll b} & 435, 740 & \text{Rhodopseudomonas (a purple bacterium)}\\ \hline \alpha\text{-Carotene} & 420, 440, 470 & \text{Leaves; red algae; green algae}\\ \hline \beta\text{-Carotene} & 425, 450, 480 & \text{Most other plants}\\ \hline \gamma\text{-Carotene} & 440, 460, 495 & \text{Green sulfur bacteria}\\ \hline \text{Luteol} & 425, 445, 475 & \text{Green leaves; green algae; red algae}\\ \hline \text{Violaxanthol} & 425, 450, 475 & \text{Leaves}\\ \hline \text{Fucoxanthal} & 425, 450, 475 & \text{Diatoms; brown algae}\\ \hline \text{Spirilloxanthal} & 464, 490, 524 & \text{Purple bacteria}\\ \hline \text{Phycoerythrins} & 490, 546, 576 & \text{Red algae; some blue-green algae}\\ \hline \text{Phycocyanins} & 618 & \text{Blue-green algae; some red algae}\\ \hline \text{Allophycocyanin} & 654 & \text{Blue-green algae; red algae}\\ \hline \end{array}$$ The Sun's $\lambda_{\text{max},\odot}$ is in the neighborhood of $500\text{ nm}$, landing it smack in the middle of all these pigments - as would be expected. I have some immediate observations:

  • Many pigments have favorable absorption in the $\sim420\text{-}500\text{ nm}$ range, near $\lambda_{\text{max},\odot}$.
  • There are a couple other peaks, from $618\text{-}680\text{ nm}$, $740\text{-}760\text{ nm}$, and $800\text{-}890\text{ nm}$. These are mainly due to pigments used by certain types of bacteria.

It stands to reason that if $\lambda_{\text{max},\odot}$ was somewhere else, different pigments would dominate. So let's add a couple columns to our first table: $$\begin{array}{|c|c|c|c|} \hline \text{Star type} & \lambda_{\text{max}}(\text{nm}) & \text{Possible dominant pigments} & \text{Possible dominant plants}\\ \hline \text{O} & 82.9 & \text{?} & \text{Algae}\\ \hline \text{B} & 145 & \text{?} & \text{Algae}\\ \hline \text{A} & 363 & \text{Miscellaneous algal pigments} & \text{Green and brown algae; some red algae}\\ \hline \text{F} & 414 & \text{Chlorophylls} & \text{Higher plants; green, brown and red algae}\\ \hline \text{G} & 527 & \text{Chlorophylls} & \text{Higher plants; blue-green algae}\\ \hline \text{K} & 725 & \text{Bacteriochlorophylls} & \text{Purple bacteria; green bacteria; blue-green algae}\\ \hline \text{M} & 967 & \text{Bacteriochlorophylls} & \text{Purple bacteria; green bacteria}\\ \hline \end{array}$$ I've stated that algae would be the most likely plants on planets orbiting O- and B- type stars. This has nothing to do with pigments; rather, it is because these stars are so short-lived that multicellular life would have a hard time developing there. In fact, age may impact the types of life you would see across the board. More massive stars have less time for higher life to develop and so probably won't lead to complicated, multicellular life.

I still have to agree, at least in part, with Ville Niemi's answer. It's clear that plenty of different pigments exist on Earth, and there's no reason to think we wouldn't see even others on an alien world around a different star. However, in drastic enough cases (especially with M-dwarfs and O and B stars), there likely would be major shifts in the dominant pigments. Perhaps new ones would develop, and I can't speculate on those. I can, though, tell you which ones would gain some slight advantages. So maybe view this answer as saying "Well, maybe [X, Y, Z]" rather than something definitive, especially given that I'm no expert.

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    $\begingroup$ The third table is too long and extends into the HNQ-part of the side. I don't know a lot about Latex. Is there a way to shrink it a bit so that it fits the available space? $\endgroup$ – Secespitus May 29 '17 at 8:59
  • $\begingroup$ @Secespitus I've tried to figure it out, but to no avail. I can try to force each cell to be multiple lines, which might do the trick. $\endgroup$ – HDE 226868 Aug 23 '18 at 3:20
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Not really. Plants generally use only a small portion of the available energy for photosynthesis and prefer frequencies that are either chemically efficient or penetrate surrounding medium, either air or water, well. This is why there are two peaks on photosynthetic efficiency graph, one is chemically efficient because longer wave lengths are easier to absorb, another penetrates water better. The spectrum of the star does not really change chemical or biological properties. Neither does it change the properties of air or water. So plants would probably still absorb only a portion of available light most convenient to them. And that part would probably be the same as on Earth.

From a comment by TimB: If your planet is in the habitable zone then you've already compensated for size and temperature by putting the planet at the correct distance from the star and the only remaining factor is the colour.

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  • $\begingroup$ Thanks. Is light the only factor? Is star size or temperature relevant? $\endgroup$ – Monica Cellio Mar 8 '15 at 21:56
  • $\begingroup$ @MonicaCellio The are quite relevant, but only in conjunction with other variables. And there are other differences between spectral classes that are also relevant, but again only in context with other variables. With all those other variables undefined... And when you add that you are asking about how the plant evolution would adapt to the differences... Sorry, but I can't even guess how to speculate. Maybe somebody else has a better idea. $\endgroup$ – Ville Niemi Mar 8 '15 at 22:27
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    $\begingroup$ Star size and temperature is what determines the light that it produces. If your planet is in the habitable zone then you've already compensated for size and temperature by putting the planet at the correct distance from the star and the only remaining factor is the colour. $\endgroup$ – Tim B Mar 9 '15 at 9:22
  • $\begingroup$ @MonicaCellio Tim B explained some of what I was trying to say with "variables", but in a form that can actually be understood. Added this comment since I wasn't sure if you get notified otherwise. $\endgroup$ – Ville Niemi Mar 9 '15 at 13:19
  • $\begingroup$ Thanks! @TimB I added your comment to the answer (with attribution of course) so that the answer proper, and not just an ephemeral comment thread, has all the important information. (Either of you should feel free to tweak of course.) $\endgroup$ – Monica Cellio Mar 9 '15 at 14:43
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I've read articles and references to scientific papers that speculate on the color of vegetation on other worlds. Even assuming biochemestry as we know it, many types of photosynthesis is possible, and can accomidate a variety of wavelengths. Add to that details of the evolutionary pressures under which the ubiquitous form evolved, and availability of elements ("interesting" catalysts use heavy metal atoms), the interaction of other tissues and the operation of human vision (not a spectrometer! Evolved for a different ambient light) and anything is possible and easily made plausible for a SF story.

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Chlorophyll is green because it is very good at absorbing the yellow light that forms most of the sun's energy. A sun with redder, or bluer light forming the bulk of the energy would preferentially produce plants that are colored differently to maximize absorption for them

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