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Aureum/golden cultivars (13 Replies)

Posted January 2, 2014 at 10:29 pm

I am curious to know if anyone has done research on the “aureum” cultivars that have needles that turn yellow in winter and turn back to green in spring. I would assume that the color change is due to the degradation of chlorophyll in the needles due to cold weather in winter which allows the underlying yellow pigment to show through. This is similar to deciduous tree leaves. In spring the chlorophyll is re-generated and needles turn green. However, I can’t find where anyone has studied this phenomenon.

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Posted January 3, 2014 at 4:53 pm

Hello there. I’m not an expert, and haven’t discovered the science behind this trait, but from what I have seen and heard, most of the ‘Winter coloring’ conifers change because of stress due to the cold. Now what exactly that cold causes in the plant is beyond my meager plant knowledge. You may indeed be on to something regarding the chlorophyll retreating deeper inside the needles, but of course different from deciduous trees, the needles don’t drop and later turn green again. Clearly it’s a genetic difference from the majority of conifers as even brutal cold/Winter cannot turn the colors of cold hardy spruce of Canada(Picea glauca/mariana). It would seem, as in nature, some natural selection has given us variation in genes in which some trees seem to be trying a new Winter survival policy. Based on reports of wind/sun scald to Gold varieties it looks like a failure in Natural selection. Hopefully one of the more knowledgable fellas around here can shed more light on this subject.

Cheers,

Will

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Posted January 3, 2014 at 6:33 pm

Thanks, Will.
If anybody knows of a good online source for a technical/scientific paper on this topic be sure to write in a link to it. As per this example:

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Posted January 3, 2014 at 6:45 pm

Dan Mosquin on the University of British Columbia Garden Forum provided the response below, but it doesn’t specifically address my question:
“Chlorophyll varies by season in the five species of temperate conifers I looked at in a quick search, all with a winter minimum (but note: not absence). Chlorophyll concentration begins to ramp up in spring, with maximum concentration in the summer and early autumn for these species.

If you have access, see: http://andrewsforest.oregonstate.edu…df/pub1632.pdf re: Douglas-fir and http://www.jstor.org/stable/1929923 for two Picea species, a Pinus and a Tsuga.

As to the gold colouration, though, I haven’t been able to track something down quickly that is authoritative.”

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Posted January 20, 2014 at 9:50 am

It doesn’t make sense to me that it is from cold stress – my Cryptomeria, for example, change color reliably every winter, and we often barely hit freezing. Also, my Microbiota change overnight (both from green to brown and back again) and seem more governed by photoperiod than temperature. This year we’ve been particularly cold, so my J. ‘Kalebab’ and Pinus strobus ‘Louie’, which don’t always turn, are bright orange and yellow, respectively. I recently purchased a Platycladus o. ‘Franky Boy’ that was shaded at the nursery on its lower half. The upper half, which was exposed to sun, is orangy; the bottom is bright green. Whatever the reason, it’s one of my favorite aspects of conifers!

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Posted January 24, 2014 at 9:34 am

I am not a researcher, and I don’t have ready access to information about research into this topic, but over the years I have had many casual conversation with professors here at Cornell about this sort of question.

Among the ideas kicked around are indeed that some amount of color change is due to less sunlight, both in terms of day length and intensity; the cold of winter might (certainly does) create some amount of stress on the plant and that could contribute to color change; soil chemistry is an interesting notion. One of the fundamental things science classes tinker with in experiments is temperature: what happens if we combine these two compounds below freezing? what happens if we do the exact same thing but above freezing, say at 34? What if we do it above boiling? So, it is an interesting question to wonder what is happening to any plant when the soil and all of it’s moisture, nutrients, micro-nutrients, are experiencing cold temperature? Is it that the color change on plant X is how it is reacting to having its soil phosphorous levels at temperature Y? Would plant Z react differently? And of course this sort of soil chemistry will vary from location to location, even micro-location to micro-location. Is the soil on one side of your driveway exactly the same as the other side?

I too would be very interested if anyone knows of who is doing real research into these sort of questions.

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Posted February 7, 2014 at 12:56 pm

I have seen several northern conifers that turn yellow in the winter: P rubens,P Marianna, and Pinus Strobus . I have all three in my yard and the degree of color appears to be greatly affected by the number of hours of direct sunlight exposure. One P mariana is a brilliant gold from Dec to May in the woods but a grafted seedling in my yard will not turn as it is in a shaded spot. I will be moving it to full sun before next winter?

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Posted February 25, 2014 at 12:42 pm

Conifer cultivars turning gold in the winter may be triggered by the plant’s entering the physiological state of winter dormancy, which is driven largely by shorter days, lower light intensity, and shift in light wavelength to far red as the sun dips lower in the autumn sky. This is supported by observation that a given conifer cultivar tends to color up around the same time each year, whether it’s been a cold fall or a warm one.

In addition to degradation of chlorophyll, another important factor is the new expression of yellow pigments, such as carotenoids. A search of a scientific search engine turned what looks like an interesting hit pertaining to species plants (Khodasevich, E. V.; Mel’nikova, L. M.; Arnautova, A. I.; Godnev, T. N. Formation and state of the pigments of conifers manifesting the phenomenon of “seasonal discoloration”. Biokhimiya (Minsk), Volume1, Pages146-9, 1973.) I could not get access to the body of the paper, but here is the abstract:

“The formation of the pools of chlorophyll (Chl) a and b and the principal carotenoids by yellowing and nonyellowing forms of conifers was essentially the same. In the 1st year of vegetation the amts. of pigments gradually increased in the spring-summer period, reaching the highest level in the autumn. In the autumn-winter period the pools of both Chl components were depleted, with that of Chl b being the most vigarous. This considerably increased the Chl a/Chl b ratio in the yellowing period. As the pools of individual carotenoids reached max values, there was a slight lowering of the proportion of the carotene fraction, but the proportions of the other yellow pigments were constant.”

I get the feeling that there has not been much study of the science behind conifer cultivars that turn gold in winter, beyond the yellowing typical of some species such as Pinus sylvestris and others mentioned above. Sounds like this could be an interesting subject for a future ACS scholarship…

Alex

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Posted December 14, 2014 at 9:59 am

Alex, thank you for your information. It makes sense!
As I write this my Chief Joseph Pinus contorta is tuning yellow!
Stu

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Posted December 14, 2014 at 10:05 am

My chief joseph on 12/ 14. 20014

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