When you say the word “autumn” surely the fallen leaves of the trees, the brown and orange colors and that crackle they make when you step on them in the street immediately come to mind. But why do the leaves fall in autumn? Although it may surprise you, the chemistry of plants is the engine behind leaf fall, a mechanism that is also related to two key concepts: self-protection and photosynthesis.
What is photosynthesis?
In the first place, leaves are plant organs that are used to carry out photosynthesis, a chemical process by which plant organisms use solar energy to produce the molecules they need to carry out their vital functions.
To photosynthesize, plants need four basic ingredients: sunlight, carbon dioxide, chlorophyll, and water. In autumn, the hours of light decrease, in addition to the fact that solar radiation is weaker, so the plants stop photosynthesizing.
Therefore, the leaves lose all their usefulness and the plant needs to spend more energy to maintain the leaves than they provide. In addition, chlorophyll, the pigment that gives them their green color, causes oxidative stress (that is, it causes the plant to age) in these light and temperature conditions. The smartest solution? Get rid of the leaves.
To do this, the Tree services activate the production of hormones that lead them to stop the photosynthesis process and initiate abscission. The ducts that carried water to the leaf is closed and, between its stem and the branch, a layer of cells begins to grow that slowly cuts the leaf without leaving any open wounds.
At the same time, the production of chlorophyll stops, so the green pigment degrades, revealing the characteristic yellow and orange colors that had remained masked by green until then.
Thus, the fall of the leaves of the trees is a self- protection and saving system that the plants activate when the leaves are no longer useful for photosynthesis. As its leaves fall, the plant enters a state of low activity, in order to reserve energy for the moment of flowering again.
In addition, when changing the leaves, the tree is carrying out a natural recycling process: the decomposing leaves transfer their nutrients to the soil, which the tree uses to sprout and grow new leaves the following spring.
Why don’t all the leaves fall off the trees?
It will not have gone unnoticed that some trees lose their leaves and others do not. What accounts for this difference?
As we have said, the fall of the leaves in autumn is a self-protection system. However, there are perennial trees that resist cold climates and low sunlight. This happens because its leaves have protection mechanisms such as waxes and resins, which resist freezing and breaking.
However, although evergreen trees keep their leaves, the photosynthesis process still stops.
The process of photosynthesis in detail
If you want to fully understand what photosynthesis consists of, you should know that it is divided into two phases. In the first phase, known as the light phase of photosynthesis, energy from the sun’s rays excites electrons in plant leaves so that water molecules (H2O) break apart. As a result, we get oxygen (O) and other chemical compounds that the plant uses during the second phase of the process: the dark phase of photosynthesis.
During this phase, a series of chemical reactions take place in which plants make the nutrients they need.
As you can see, photosynthesis is not only a vital mechanism for plant organisms but it is also essential for the rest of living beings. We must take care of our plants and our trees since these, by absorbing carbon dioxide and returning oxygen, are essential for the health of the planet.
In fact, its way of producing energy through photosynthesis is so efficient, clean and sustainable that scientists are currently investigating the development of infrastructures that produce energy through the same process. In this way, the fuel would not generate CO2 and therefore would not contribute to global warming and would reduce our dependence on fossil fuels.
At the same time, the production of chlorophyll stops, so the green pigment degrades, revealing the characteristic yellow and orange colors that had remained masked by green until then.
Thus, the fall of the leaves of the trees is a self- protection and saving system that the plants activate when the leaves are no longer useful for photosynthesis. As its leaves fall, the plant enters a state of low activity, in order to reserve energy for the moment of flowering again.
