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Tuesday, October 4, 2016

How to Read Red Aspen Leaves: Anthocyanins and Sun Block for Leaves

     Why do some aspen leaves turn orange or red, rather than the more usual yellow or golden? Maizie, fearless and happy pup, and I were on our 16th annual autumn pilgrimage to Hell's Hole Trail on Saturday, pondering this very point.



      Since we've hiked the same trail on or about September 30th for 16 autumns, we've seen the same aspen tree turn yellow one year and bright orange or red the next few years, and back to yellow for a few years, then back to orange.


     
       I wrote in a 2014 PEOTS postscript (after my sign off) about it being a very orange year (lots of carotenoids). 2015 was overall much yellower; the reds and oranges were quite rare.  How much does moisture, temperature, soil conditions, or other factors affect the yellow, orange, or red of aspen? Ready, Maizie? Lead the way!



     
      First, a brief photosynthesis review: As deciduous trees prepare to lose their leaves, they begin to resorb nutrients and to slow chlorophyll production, unmasking other pigments that have been present all along. Yellow and orange leaf colors are due to xanthophyll and carotenoid pigments (see below).

Here's a handy chart showing all the leaf pigments:


  • Chlorophyll for greens
  • Carotenoids for orange
  • Xanthophyll of the Carotenoid group for yellow
  • Anthocyanins for reds and purples
  • Tannins for brown as a waste product

      Reds and purples, as noted above, are due to anthocyanins and these pigments are only produced in the autumn (by some plants). It is still not clear the role these red pigments play, and why a tree would spend energy to create them at a time when they are about to drop all their leaves. Hypotheses include reducing the risk of light-induced damage to leaf cells (sort of a sun block for the leaves), protection from cold, protection from insects, and helping leaves retain water.



        Some plants almost always produce red but, in some cases like aspen, only a few trees turn red. What makes them different?



      In 1989, Kuo-Gin Chang and his research team, then at Colorado State University, analyzed the pigments of yellow and red aspen and determined that all aspen produced carotenoids, but anthocyanins were only found in red aspens. The ability to produce anthocyanins appears to be a genetic trait that some aspen trees have, but most don’t.



      However, just because a tree can produce anthocyanins doesn’t mean that it always will. The researchers followed the trees they studied for five years. The trees that started off yellow stayed yellow, but some of the trees that started off red (i.e., they produced anthocyanins) were yellow in subsequent years. This demonstrates that both genes and weather cause the red. Years that produce the best reds have warm sunny autumn days followed by cool, but not freezing, nights.




      Not only do the red pigments of the anthocyanins protect leaves from the sun they also give some species extra time to absorb their essential leaf nutrients. As chlorophyll starts to exit the leaves, anthocyanins are being created to get the leaves additional time to unload the excess nutrients. Anthocyanins are a result of excess sugars within the cells and in combination with bright light, produce red pigment. Most anthocyanins are present only in autumn. One may observe a tree turning red at first and then changing to all yellow as days lengthen and rains come. The trees then need more food supply so they go into high gear and the leaves turn yellow.




       So, clearly, Maizie and I need more data within one season to see if the reds and oranges of certain aspen turn yellow later in the autumn.

Leaving it there for now; how's your aspen?
Steph
       
       

33 comments:

  1. Not a very colorful fall in NJ this year, at least according to my non-colorblind wife. Until this week, it's been very dry.

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    1. Oy, I would be most displeased to be colorblind. Have you ever been able to see all the colors of autumn? Or any gradation?

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    2. Ah, yes, now I remember. . .

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  2. Follow up on the predicted southern California earthquake. I was hoping the predictive tools would be correct (but with no loss of life or major damage). The warning expired today. 10-4, good seismic buddies...

    We did have a shallow (3 mi) earthquake here in Evergreen, CO, this week. It was a 2.4 on the Richter Scale.

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  3. The bells are ringing at Smith College. It's Mountain Day! Time for foliage, biking, hiking and apples.

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  4. "Foliage" from Latin for leaf, hence also folio. Alternate spelling, foilage (which seems wrong to me)

    Al U. Minium

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  5. While out running a couple weekends ago, I passed several trees (don't know which kind)that were mostly yellow, but with a relatively large red patch.

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    1. So, I wonder if the red patch was more stressed from sun or bugs or whatever. And will the red leaves turn yellow as fall goes on. . .(Please report back, David.)

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  6. Hmm, I don't remember any "Mountain Day" bells ringing at Smith, the one fall term that I was there, that is....

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  7. ViolinTeddy, hmmmm, it's a tradition dating back to 1877 (almost as long as the College) so I'm not sure how you missed it. Perhaps you were away for a long weekend?

    It's a huge deal, with students and profs trying to predict when it will be based on when the Art 100 mid-term is and weather and all sorts of factors. It was a major topic of conversation at dinner in late September-early October.

    Now the students have all sorts of predictive tools and apps and formulas to guess when Mountain Day will be. It is totally up to the College President.

    It must be where my love of this time of year comes from! Hope you can have a Mountain Day where you are and head outside for the day, apples in hand.

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    1. I posted this Mountain Day Notables Singing video on a previous Mountain Day, but since you are relatively new to PEOTS. . .and since you missed Mountain Day while you were there :-(. And, since you are musically inclined!

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  8. Phantastic photos, Steph. I especially like the very first one, of the intrepid Maizie surveying the aspen landscape.

    "Years that produce the best (aspen tree) reds have warm sunny autumn days followed by cool, but not freezing, nights"...
    Yhis reminded me of ideal condition for maple trees to produce sap for syrup in the spring.

    LegoLobbiesForLessAspensMore-LaMaples

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  9. Thanks for that sappy offering, Lego.

    It is interesting that prolific running sap also correlates with the same conditions for red leaves in aspen (and other trees).

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  10. Yay! Mountain Day! I was actually in North Adams, MA on that day and the weather was glorious. Foliage is late, though, this year. I was in town for the Fall Foliage parade, which is always the first Sunday in October and used to be near peak foliage when I was a child, but now with global warming, not even close.

    I hope to reblog this to Top of JC's Mind, but will have to do it by link. I wish Wordpress played better with your platform so that people could see your lovely photos to encourage them to come visit.

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    1. Hurray, Joanne, and thanks for the reblogging. Glad you were able to be in North Adams and celebrate the later foliage. Friends in Maine say it is peak foliage there this weekend.

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  11. Have you seen this?

    If I screwed up the link, http://fivethirtyeight.com/features/the-secret-lives-of-rocks/.

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    1. David, what a cool link! Thanks.

      {I have a wee bit of trouble with the concept of rocks having lives, secret or not, but the concept of a toddler asking is great.}

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  12. It was raining on Sunday, so instead of going out for a bike ride, I used my stationary bike while I watched a couple of Jeopardy episodes from last week. Came across this:

    DIAMONDS ARE FOREVER

    Over 40 carats, the largest diamond found in the U.S. was discovered in 1924 in what is now this state's Crater of Diamonds.

    News to me. It's in Murfreesboro, Arkansas.

    Then, today, I found this article about how a father and daughter found a two carat uncut diamond there.

    These things always come in threes, so I'm waiting for another lightning strike...

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    1. What a cool find!

      My friend is leaving this morning for a Diamond Anniversary party. Does that count?

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    2. Yeah, that's gotta be the third one.

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    3. She is headed to Floral, Arkansas, a teeny unincorporated place.

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  13. I was thinking about the fossil syrinx news for this week's post. Very exciting stuff.

    Vegavis iaai is a great name for the critter with a syrinx. Sounds melodious with all those vowels!

    Maybe Siri ought to be Syri. Great clip, btw.

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  14. This blog's at least partially about literature. How about some griping about today's Nobel prize? I like Scottish novelist Irvine Welsh's reaction on Twitter (via the AP):

    "I'm a Dylan fan, but this is an ill conceived nostalgia award wrenched from the rancid prostates of senile, gibbering hippies," the "Trainspotting" author wrote.

    He continued: "If you're a 'music' fan, look it up in the dictionary. Then 'literature'. Then compare and contrast."

    He also begged to know if writer Don De Lillo had been inducted into the Rock 'n' Roll hall of fame yet.

    -----

    I sent that to my son, the economist, who liked it and replied:

    I'm always grateful to the literature and peace prizes for making economics only the third-sketchiest Nobel prize. That's only slightly above the median level of sketchiness!

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    1. The tweet pegged it, except not all those hippies have prostates.

      Your son's response was (train) spot on!

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  15. New post on "Vinicunca Rainbow Mountain in the Andes of Peru: Dr. Seussian Stripes" is now up. Challenge: see if you can find it on GoogleEarth!

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