Ran into this in the front ranges in Alberta. I'd not noticed red willows before this. The shot is at an elevation of 5400 feet. Just high enough that poplar are absent. The ground cover on valley floors is overwhelmingly a mix of autumn willow and dwarf birch. The willow in this area is just starting to fluff. Some plants still have intact seed capsules (correct term?) Others are masses of seed hairs getting ready to set sail. I snapped this shot because it had an unusual concentration of red leaves, but red leaves appeared in various willows in this area. As you can see from the large picture, predominantly end leaves are affected. This fits with many other fall colour shifts, that leaves with a clear view of the sky are chilled more. How unusual is this? It was too common to be a branch sport. So my guess right now is that it has to be just the right combinaton of micro climate, or a virus. Thoughts?
I don't think it's too uncommon, particularly for high elevation plants (or low elevation plants in the arctic). The pattern of it occurring on end leaves is also not unusual -- these will just be slightly more exposed to the triggers for winding down of chlorophyll (and, ramping up of anthocyanins).
I have about 2 dozen other willows at my farm. The closest any of these have ever come is that flame willow (Golden willow x something...) will have fall leaves with an orange yellow. It was only a few patches that showed this effect. Most of the rest of the willows were yellow at the top and green underneath, which is what I would expect in terrain that is getting fall frosts. By comparison the dwarf birch was all bright orange. At slightly lower elevations, aspen was about half yellow leaves. (Aspen didn't grow at the elevation I saw these.
Do you have access to this paper? Anthocyanin Biosynthesis and Degradation Mechanisms in Solanaceous Vegetables: A Review Scroll down to Environmental regulation of the anthocyanin pathway , it leads with:
Yes. I have access. Thank you for the article, and your extraction of that line. The article is tough reading. I don't have a recent enough genetics course, nor any biochemistry. It's enough to make my eyes cross. Most of the article spoke of solanaceae and petunias. But it also mentioned that anthocyanin pathways were strongly conserved. From that I infer that there should be some general applicability. Things I picked up: * Moving from an acidic to neutral environment can decolourize anthrocyanins. So the patch of red tip willow may be in more acid soil. Easy enough to check. * I found the reference you made above. I've also read elsewhere, but not in a peer reviewed article, that one of the functions of anthocyanins was the prevention and remediation of UV damage. At an elevation of around 5000 feet there will be substantially more UV. That said, nothing in the article other than the pH comment explains why this colouration wasn't universal, or at least much more common. I saw red leaf willows dotted through the landscape for about half a km. The rest of our path (some 25 km of montane meadows) was yellow willow and orange birch. Are purple leaved trees, such as Schubert Chokecherry, and the raft of coloured ninebark shrubs due to a regulation failure? Some gene that says, "That's enough" doesn't get expressed?
Oh, much of that article is a hard slog for me as well, I really wanted to point out the environmental regulation. I wouldn't spend time trying to determine whether the willows are growing in more acidic soil -- that bit will be more in reference to the pH within the cell, which is regulated and homeostatic (kept consistent) by hydrogen ions in and out of the vacuole. You could be seeing different species of willow at that elevation, one which does colour into red and one which doesn't. Or, this could be due to other microclimate factors like soil moisture. Purple-leaved trees and the like are indeed due to generation and persistence of anthocyanins (which are also stored in the vacuole...). Regulation failure preventing overproduction seems likely as one of the ways this could happen, but I suppose there could be other mutations that prevent breakdown or sequester the pigments in other parts of the cell where they can't be broken down, etc. etc. I don't know enough.
The Sierra Club Engagement Calendar had an autumn color shot of a single scarlet red aspen in the center of a bunch of the usual yellow one year. Wherever that variant was located somebody should have gone there and collected clonal propagation material, put any resulting plants into circulation.
There are red/pink aspens in circulation. Outfit in Colorado sells them but won't ship over the border. Aspen, unlike many other poplars, do not readily root from cuttings. Usually you propagate aspen clones from roots, or by tissue culture. I have had swedish aspen turn scarlet, but I was also having problems with bronze leaf disease in that group. Not sure if this was a side effect of the fungus. And aspen will sometimes have a few leaves that go red.
