What determines the blue and yellow color of the needles? The blue color arises from the special light scattering properties of the sheet surface. The plant synthesizes special waxes that protect the needles from moisture loss or excessive light. Pure wax is transparent, and if the surface is smooth, it gives the leaves a slight sheen. However, if the wax is deposited in the form of microscopic flakes, the surface looks whitish, since a lot of light is scattered. Here you can draw an analogy with glass: smooth glass is transparent, but if you rub it with sandpaper, microscopic scratches will appear and the surface will become dull.
In plants, green leaf tissues lie under a translucent layer of waxy scales. The dark green color in combination with wax flakes gives the effect of a blue color. The wax coating is easy to wipe off, and then green fabrics will appear underneath.
A yellow color is obtained by changing the ratio between the pigments in the sheet. The main pigments of photosynthesis in junipers (like other green plants) are blue-green chlorophyll a, yellowish green chlorophyll b and yellow-orange carotenoids... An increase in the proportion of chlorophyll a leads to an increase in the dark green color. If there is more chlorophyll b and / or carotenoids, the color becomes more yellow. This is due, as a rule, to single mutations, which are not always favorable for photosynthesis. Complete loss of any of the pigments can be fatal to the plant.
Why do junipers “bronze” by winter? The composition of the pigments and the structure of the wax change during the season. This is done to ensure that the composition of the pigments is "matched" to the light and temperature. The well-known saying “in spring and summer - in the same color” does not always apply to junipers. The color of their needles changes throughout the year, this is especially noticeable during a cold snap or during a period of intensive growth. In addition to photosynthetic pigments, plants can form anthocyanins - Substances of red-violet color, participating in protection from ultraviolet radiation. Anthocyanins are also synthesized during drought and low temperatures. Their appearance indicates that the plant is preparing for unfavorable conditions. The combination of the green color of chlorophyll with the reddish tint of anthocyanins gives the characteristic autumn-winter "bronze" color of the juniper needles.
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