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Why Do Plant Leaves Turn Red?

When we think of plant leaves, the color green naturally comes to mind, right?

However, some plants change from green to red. It’s quite fascinating! Deciduous trees like the Maple beautifully turn red before shedding their leaves.

Succulents often turn their leaves red as it gets colder. And if you expose plants like Bromeliads to sufficient sunlight, they’ll develop a stunning red hue.

So, Why Do Leaves Turn Red? 

There’s actually a reason behind it. Inside the cells of a plant’s leaves, there are chloroplasts containing chlorophyll, and vacuoles with carotenoids and anthocyanins.

Chlorophyll gives leaves their green color, which is why most leaves appear green. Carotenoids are yellow, like the vivid yellow of Ginkgo leaves.

Anthocyanins range from red to purple and are well-known antioxidants found in blueberries, synthesized within the leaf cells.

Chemically, the photosynthetic process in plants involves two reactions:

  • Converting light into energy for survival.
  • Using some of this energy to convert carbon dioxide, creating sugars for more energy storage.

Most plants conduct these two processes simultaneously. However, succulents separate them between night and day.

Environmental factors can increase or decrease the amount of these reactions. Sometimes, if the first reaction predominates due to certain conditions, part of the solar energy turns into reactive oxygen species.

This can happen, for example, when a plant gets sunlight in cold conditions or during its growth period, just as I initially explained.

You might have heard of reactive oxygen types. They’re known to contribute to aging in humans, but they also negatively affect plants by inhibiting photosynthesis.

To combat this, plants synthesize anthocyanins, acting like sunglasses to reduce the amount of the first reaction and protect the chloroplasts.

Now, you might wonder if turning red is bad. Actually, red leaves are not inherently harmful. In fact, in horticulture, red leaves often add to a plant’s aesthetic value and enjoyment.

Conversely, poor sunlight exposure can lead to plants having darker green leaves, elongation, or unnecessarily large leaves, which can reduce their horticultural value.

Maples, for instance, undergo a different mechanism for their autumnal color change. As winter approaches, plants prepare to shed their leaves.

Lower temperatures weaken the leaves’ functions, leading to the breakdown of chlorophyll. Interestingly, this broken-down chlorophyll is recycled back into the stem as nutrients.

Then, a layer called the abscission layer forms at the base of the petiole, hindering material exchange.

The remaining sugars in the leaves produce the red pigment anthocyanin, turning the leaves red – this is what we know as autumn foliage. Eventually, the leaves are detached at the abscission layer and fall.

Understanding these factors that turn plant leaves red can be really helpful. Whether you’re trying to cultivate a certain look or simply monitoring your plant’s health, this knowledge can guide you.

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