Leaves: Part 1 – Why leaves change color?

By September 15, 2017 No Comments


Leaves in nature comes in a large variety of sizes and shapes, and they all plays an important part in nature, since they forms an important system called photo synthesis.  Photosynthesis is when leaves absorb water from the soil and carbon dioxide from the air and transform it into oxygen and glocose (sugar) in the form of fruit.  The size and shape varies from one tree species to another.  Although when take it foregranted that leaves are green, there are other species that have a different color or have the ability to change color.  Talking about leaves is a vast subject, so we decided to divide our informatin in two parts:  Part 1 will be dealing on why leaves change color, and Part 2, our next blog, we will be talking about in a more practical way on how to reduce the leaf size with most of our bonsai trees.

Japanese Maple

One of the most popular trees in bonsai is the Japanese Maple and one great reason for its popularity, apart from its nicely designed leaf, is that it has the ability to change the color of their leaves as autumn approches.  The change in color from green leaves in spring to golden yellowish and brown, is common to other species too.

In this chapter, we will not be dealing with a scientific paper but about the facts that happens in simple words, to help the bonsai lover or enthusiast to understand this principle of color change and why it happens.

Why are leaves green?

Let’s start by understanding why leaves in plants and trees look green.  The answer for this first question is simple: Chlorophyll.  Chlorophyll consists of a green pigment that gives the leaves their natural color.  Chlorophyll, that is the green pigment inside the leaf will absorb the red and blue rays of light to do the photosynthesis, and reflects back the green light.  It is the reflected green light that gives the leaves their distinctive color.  The chlorophyll does not absorbs the green light.

Color pigments

Plants might have one of the three major different types of color pigments:

  1. Chlorophyll
  2. Carotenoids
  3. Anthocyanins

Chlorophyll:  A dominant pigment that gives leaves their green color, which is very important for photosynthesis process, were, plants uses sunlight to manufacture glucose as their food source.

  • During photosynthesis, the leaves absorb sunlight to change carbon dioxide and water into glucose and oxygen.

Carotenoids:  A plant pigment responsible for bright red, yellow and orange hues in fruits, flowers and vegetables. They play an important role in plant/tree health.

Anthocyanins:  A water soluble pigment that gives the red, purple, or blue color.  The change in hues of the anthocyanin varies according to the water pH in the leaf.  Fruits like red apples, grapes, blueberries, cherries, strawberries, and plums are the results from the presence of the anthocyanin pigment.

Change of color of leaves

Chlorophyll is constantly produced in spring, thus the yellowish green of the new leaves, and when the night time increases in autumn, the chlorophyll starts to decreases until it stops being produced.

  • This is the main reason why leaves change color.
  • The carotenoids and anthocyanins are also present in spring, but chlorophyll  pigment dominates their presence.
  • When chlorophyll reduces in autumn, both the carotenoids and anthocyanins will show their presence showing their colors.

What makes leaves to fall?

Sunlight intensity will start declining in autumn when the days also gets shorter.  Leaves feel this change and they start a process that will lead to their fall.

  • The veins which normally are full of fluids shuts of a layer of cells trapping sugars inside.
  • This will promote anthocyanins, which produces a red pigment.  This is the reason why the change in color of a leaf before falling of the tree.
  • Once the connection is sealed off, the leaf will fall.

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Martin Abela

Author Martin Abela

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