Every year about this time, I get asked by my friends and clients the same question, What makes the leaves of trees turn color in the fall? For years, I regurgitated the same old message of which chemicals are responsible for which color and how chlorophyll masks these colors in the spring and summer without giving it too much further thought.
Realizing that everything in Nature happens for a specific reason ad understanding that trees do very little that is wasteful, I decided to explore this concept a little further.We know that carotenoids produce the yellows, orange, and brown colors and that anthocyanins produce the reds. We have known that both chlorophyll and carotenoids are present in the chloroplasts of leaf cells throughout the growing season.
Further, it was thought that most anthocyanins are produced in the autumn, in response to bright light and excess plant sugars within leaf cells. The whole process in fact is one of protecting the leaves as much as possible while the leaves go through a process called senescence. The current theory holds that the anthocyanins shade the senescing leaves from the bright sunlight that then allows the leaves to recover foliar nutrients ( the resorption protection hypothesis.) Anthocyanins have been shown to be effective light screens and therefore protect the photosynthetic components of the leave during senescence.
Recent experiments carried out by Dr. William A. Hoch, Dr. Eric L Singhass, and Dr. Brent H. McCown (University of Wisconsin) have come to some interesting conclusions. Low temperatures significantly reduce the capacity of plants to photosynthesize light into energy. The northern most selections of trees had the highest levels of these protective pigments.
This leads to the conclusion that anthocyanins are more important trees that evolved in northern climes more so than trees in warmer climates. A direct correlation in the amount of anthocyanins in senescing leaves was noted as the researchers looked at trees that grew in colder climates.
It was also interesting to discover that trees in the wild were able to senesce (or reabsorb) the soluble nitrogen from their leaves far more efficiently than the hybrid or improved cultivars in high stress environments. The recovery of nitrogen by wild (or native) species was almost twice that of “improved varieties.”
The end result of this work has left more questions to be answered. If plant breeders select clones of trees for bright red fall color will these trees then perform in warmer climes? Or will they be better adapted to low nutrient and colder climes?
The one conclusion they all agree upon is that the fall pigmentation we see in leaves shield the leaves from the harsh autumn light as the tree attempts to recover critical foliar nutrients.
Realizing that everything in Nature happens for a specific reason ad understanding that trees do very little that is wasteful, I decided to explore this concept a little further.We know that carotenoids produce the yellows, orange, and brown colors and that anthocyanins produce the reds. We have known that both chlorophyll and carotenoids are present in the chloroplasts of leaf cells throughout the growing season.
Further, it was thought that most anthocyanins are produced in the autumn, in response to bright light and excess plant sugars within leaf cells. The whole process in fact is one of protecting the leaves as much as possible while the leaves go through a process called senescence. The current theory holds that the anthocyanins shade the senescing leaves from the bright sunlight that then allows the leaves to recover foliar nutrients ( the resorption protection hypothesis.) Anthocyanins have been shown to be effective light screens and therefore protect the photosynthetic components of the leave during senescence.
Recent experiments carried out by Dr. William A. Hoch, Dr. Eric L Singhass, and Dr. Brent H. McCown (University of Wisconsin) have come to some interesting conclusions. Low temperatures significantly reduce the capacity of plants to photosynthesize light into energy. The northern most selections of trees had the highest levels of these protective pigments.
This leads to the conclusion that anthocyanins are more important trees that evolved in northern climes more so than trees in warmer climates. A direct correlation in the amount of anthocyanins in senescing leaves was noted as the researchers looked at trees that grew in colder climates.
It was also interesting to discover that trees in the wild were able to senesce (or reabsorb) the soluble nitrogen from their leaves far more efficiently than the hybrid or improved cultivars in high stress environments. The recovery of nitrogen by wild (or native) species was almost twice that of “improved varieties.”
The end result of this work has left more questions to be answered. If plant breeders select clones of trees for bright red fall color will these trees then perform in warmer climes? Or will they be better adapted to low nutrient and colder climes?
The one conclusion they all agree upon is that the fall pigmentation we see in leaves shield the leaves from the harsh autumn light as the tree attempts to recover critical foliar nutrients.
SHARE
