I would like to know if anyone understands the reason that the so-called "golden/aurea" cultivars of pines, spruces, junipers, etc. turn yellow in the winter and then green in the spring/summer/fall? I assume that the chlorophyll in their needles dies off in cold weather and shows an underlying yellow pigment. This yellow pigment is obscured in the spring when the weather warms and the tree becomes physiologically active. Has anyone studied this in detail?
Chlorophyll varies by season in the 5 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/pubs/pdf/pub1632.pdf re: Douglas-fir and http://www.jstor.org/stable/1929923 for 2 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.
Thanks so much for the info and articles, Dan. I will post photos of two of these yellow cultivars to give you an idea of how yellow they become in the winter and presumably how little chlorophyll is left. The left one is Pinus contorta var. latifolia "Chief Joseph". The right one is Pinus sylvestris "Gold Coin"
