杏吧原创

Q: My garden has a tree whose leaves are a rich wine-red colour all year
round. I thought that chlorophyll was green. If so, how does this tree
photosynthesise? Is the red variety less efficient and therefore less
common?

A: Your tree is certainly not lacking chlorophyll, a pigment which is very
important in photosynthesis and without which the tree simply could not
survive. The green colour of chlorophyll is simply being masked by one of a
number of other pigments not involved in photosynthesis, including flavins and
carotenoids, which are present in abundance in certain species of plant.

Carotenoids are yellow and orange (they give carrots their orange colour,
hence their name) or orange/red in colour, so probably contribute to the red
colour of leaves, but the richness of the red colour is provided by flavins.
These are a group of photoreceptor chemicals which absorb blue wavelengths of
light from the spectrum of wavelengths present in white light and emit all
other wavelengths, making the pigment appear red. This blue light controls
several reactions in the plant, including the biosynthesis of pigments,
carbohydrate and protein metabolism and photomovement (growth movements of
shoots and roots in response to directional light, gravity, and so on).

A: The assumption that chlorophyll is green is a correct one, but leaves
have a number of colour pigments in them, hence when the chlorophyll
decomposes in autumn they turn a variety of other colours. Very strong colours
mask the green of chlorophyll, but photosynthesis still takes place (red,
brown and even blue seaweeds photosynthesise). Trees such as you describe are
鈥渟ports鈥�, nursery creations grown for show. They are less efficient and in the
natural world would be very scarce as trees with green leaves would easily
outcompete them.