Why Do Leaves Change Color During Autumn?

Many people feel happy to see changes in the color of leaves in the garden during seasonal changes, which is a natural process and leads to the falling of leaves at the end of the fall season.

Why Do Leaves Change Color During Autumn? Leaves change color during autumn due to chemical changes when the chlorophyll breaks down as days get shorter and temperature drops. Xanthophyll, carotenes, and anthocyanin are responsible for yellow, orange, red, and other combinations of colors.

The plants take almost a few weeks to change their foliage color, but some trees do it quickly when the climate and weather conditions favor accessory pigment expression.

Typically, the trees in cooler and humid regions undergo seasonal changes faster than those in warmer areas with low moisture content.

Why do leaves change color in autumn?

Many alterations occur in plants with seasonal changes that can also affect the appearance of leaves by changing their color and texture.

A chemical change in the plants leads to variations in leaf color, which is referred to as autumn foliage. It is a visual indicator of the fall season’s arrival that affects the photosynthesis rate.

In addition, plants need sunlight to carry out photosynthesis because chlorophyll captures light energy and transfers it to plant systems to produce oxygen.

Day length decreases in autumn as days get shorter and the nights are longer, so plants cannot get enough light for photosynthesis.

The sunlight activates chlorophyll molecules by energizing its electrons, which can capture energy from light and pass it to the plant’s internal systems.

The amount of chlorophyll or green pigment reduces in fall when the leaves absorb less sunlight. Accordingly, the foliage loses its green color and appears in different shades.

There are four types of pigment in leaves, but chlorophyll suppresses other accessory pigments during spring and summer, giving a greenish hue to the foliage.

However, other pigments can express in the absence of chlorophyll and display their color on the foliage when there is not enough sunlight to activate chlorophyll.

Other environmental stressors, like low temperature, also promote chlorophyll breakdown because it needs around 30 degrees Celsius to carry out its function.

However, the temperature in autumn ranges between 19 to 25 degrees Celsius, which alters the production of green pigment and triggers the expression of other pigments.

So, you cannot see green leaves in the fall season due to changes in external conditions, but they can restore their original color in summer and spring when the temperature gets normal.

What color appears on leaves during autumn?

Plant leaves contain four different pigments, while the most common is chlorophyll, which is usually expressed in the summer and spring seasons and gives a green pigment.

The green pigment masks other pigments until it is produced in large quantities but begins to break down in autumn. This leads to the expression of accessory pigment in the leaves.

In addition, the accessory pigments include carotenoids and anthocyanin, which are responsible for producing red, orange, yellow, and different combinations of these colors.

Many types of carotenoids, including xanthophyll and carotenes, produce red, yellow, orange, and other bright shades in plants.

The anthocyanin pigment belongs to a phenolic group and gives them a splash of red color. Leaves and fruits appear blue, red, and purple after the expression of anthocyanin pigment.

Moreover, the foliage appears yellowish in the early autumn and turns red when the temperature gets lower in the late fall because anthocyanin is expressed at low temperatures.

This pigment can also produce a shade of purple and red due to the increased content of sugar in the leaves, which forms anthocyanin.

The foliage colors in autumn are bright, warm, and neutral, as you can see them in olive green, mustard yellow, ivory, pumpkin orange, brown, cream, and eggplant purple.

What happens when leaves change color during autumn?

Many morphological changes become visible in the plant leaves during autumn that look impressive as bright or vibrant colors make them look beautiful.

However, other internal modifications occur when the days get shorter and colder. The production of auxins reduces, which affects the growth of plants, elongation, flowering, etc.

Accordingly, a lower concentration of auxins puts stress and weakens bonds between the branch and leaf. This results in the breakage of the leaf from the branch and falls to the ground.

Their color determines nutritional value because alterations in the availability of nutrients have a direct impact on the foliage. Only green leaves are considered healthy or nutritious.

In the same way, the change in color of foliage makes it less attractive to predators as they avoid eating red or purple leaves by assuming that they have low nutritional value.

So, the plants do not remain as attractive as they are in the spring and summer seasons when the green pigment appears.

What factors affect the change in leaf colors in autumn?

Autumn foliage varies in plants belonging to different species as some trees, like the maple tree, show a colorful display of bright or intense shades of red, known as royal fall foliage.

However, the oak trees remain bright and attractive for a long, but the maple trees do not have a longer duration of fall shades.

Moreover, the temperature also affects their duration and intensity, as cool weather prolongs the overall duration and makes them look brighter.

The humidity level is also a prominent factor because they can maintain bright foliage for a long if there is adequate moisture in the environment.

Their age also plays a role in the extent of changes in color as young leaves remain attached to the tree while the older ones blow away quickly.

Furthermore, the light intensity and length of days also change their duration and intensity because the lower light intensity and exposure can make them look dull.

What type of plant leaves change color during autumn?

There are two different categories of trees, deciduous and coniferous, divided on their response to changing climatic conditions and morphological characteristics.

The deciduous trees are not evergreen plants as their name indicates “temporary,” which means their foliage changes color in autumn and falls off.

These flowering plants shed their leaves yearly because the changing climates affect the amount of chlorophyll in foliage and trigger other pigments.

In contrast, coniferous trees can keep their leaves all year and do not change foliage color because they do not contain all pigments present in deciduous trees. 

They can only appear brown or green after falling on the ground because their needles have a waxy coating on the surface that protects them from changing climatic conditions.

Moreover, these trees have broad leaves and larger sizes, unlike evergreen coniferous trees, with smaller foliage and short stature.

The climbers and shrubs appear different in autumn and attain magnificent shades of orange, yellow, and red. Such plants and trees respond to changing seasons by changing foliage color.

Furthermore, dogwoods, oaks, maples, magnolias, cherries, ash, poplar, elm, and many other trees in temperate and tropical climates go through autumn foliage.

So, only deciduous trees change their color seasonally, but it becomes visible in the fall seasons when the bright red or yellow pigment appears.

Related Articles:

Why are plants not invertebrates?