We all love the colors of autumn leaves. The vibrant foliage adorns our lives. But have you ever wondered why leaves change color in the fall?
Why do maple leaves turn red? Where do the red and orange hues of fallen leaves come from?
To answer these questions, we must first understand the function of leaves.
Photosynthesis
Leaves are nature's food factories. Plants draw water from the soil and carbon dioxide from the air. Then, using sunlight, they convert water and carbon dioxide into oxygen and glucose. Oxygen is the gas we breathe, and glucose is a type of sugar.
Plants use glucose as an energy source, much like food for them, essential for their growth. The process by which plants convert water and carbon dioxide into oxygen and glucose is called photosynthesis, meaning "synthesis using light." Chlorophyll, which gives leaves their green color, plays a crucial role in photosynthesis by absorbing sunlight, essential for the plant to convert carbon dioxide and water into glucose and oxygen.
Preparing for Winter
In winter, there isn't enough sunlight and water for photosynthesis to occur. Many plants rest during this season, relying on the food reserves they stored during summer to survive, the "food factories" of many plants shut down, and chlorophyll disappears from the leaves.
When the green fades away, we see the leaves turn yellow and orange. In fact, these colors have always been present in the leaves; they are just not visible during summer because chlorophyll masks them.
However, red colors emerge in autumn. In some trees, like maple trees, when photosynthesis stops, glucose is trapped in the leaves. Sunlight and cool autumn nights cause this glucose in the trees to turn red. Additionally, the brown leaves of trees like oak are the result of some metabolic waste in the leaves. It is these substances that make fallen leaves colorful!
Plants spend the whole summer preparing for autumn and winter. But how do they survive winter? In winter, days are shorter, and there's less water. Plants must devise clever ways to survive.
Some plants, like many annual ornamental flowers, have a special strategy. "Annual" means that the lifecycle of these plants is one year; they won't live to see the next year. When winter comes, they wither away. But because they've left behind seeds, those seeds will sprout the following year.
In contrast to annuals, there are perennial plants, which have a lifecycle of at least two years. Many trees, shrubs, and herbaceous plants with soft, fleshy stems are perennials. When winter arrives, the woody parts of trees and shrubs can withstand the cold. The above-ground parts of herbaceous plants, like leaves and stems, wither, but the underground parts (roots and bulbs) survive. They rely on this method to survive winter.
These plants shed their leaves and grow new ones the following year because insects, diseases, and weather gradually damage the leaves. Deciduous trees like maples, oaks, and elms are perennials that shed their leaves in autumn to prepare for winter.
Then there's a category of plants that retain all their leaves in winter, known as evergreen plants. Their leaves are special, capable of withstanding cold and dryness.
Pine and fir trees are examples of these evergreen plants, with needle-like leaves. Some evergreen plants have broad leaves with rough, waxy surfaces, like holly. In cold, dry seasons, their leaves curl up to reduce surface area, thus minimizing water loss. As long as there's enough water, evergreen plants undergo photosynthesis in winter, although at a slow pace.
In the grand stage of nature, autumn is a colorful show, where leaves, swayed by the autumn breeze, display a magnificent array of colors. It's not only a splendid spectacle of nature but also the culmination of the wisdom and survival strategies of plants. From photosynthesis to the transformation of leaf colors, every detail showcases the marvels of nature.
May we learn to cherish and be grateful for our harmonious coexistence with nature, just like the autumn leaves, radiating our splendid brilliance.
