Home / Grow Light Advice / The Effect Of UV Light On Plants

ultraviolet light and plantsPlants, like humans, are living organisms; and just like us they require nutrients and the right conditions to flourish. While plants obviously need water to survive, it is light that is their main source of energy.

The natural light we enjoy here on earth comes from the sun, a blazing mass of fire that produces enough energy to maintain all life forms on this planet. The light from the sun is composed of packets of energy called photons; it is this energy that plants utilize to make their food supply.

The light from the sun is made up of varying wavelengths. Plants use most of this spectrum, some colors far more than others, but they do not make use of ultraviolet and infrared light.

Does this mean that UV light has no effect whatsoever on plants? Quite the opposite. Varying levels of UV light bring about distinct characteristics in crops. Unfortunately, most of them are negative.

 

What is UV light?

Ultraviolet light is invisible to the naked eye and is the shortest wavelength in the spectrum lying between 100 to 400 nm (micro moles). Before UV light reaches the earth’s surface, most of it is absorbed by the stratosphere.

The earth’s atmosphere is well-adapted to absorb all UV-C radiation, but UV-A and UV-B light still reaches the earth’s surface. Luckily, this light is not too harmful at the levels that reach us.

It is UV-R light that is most damaging to life forms. Thankfully, only 7-9% of it is able to reach the biosphere. For this reason, under normal conditions, UV light does not have a substantial impact on plant growth. The exact effects of UV light have been evaluated under laboratory conditions, however.

 

Impact of UV Light on Microbes

Microscopic organisms such as bacteria play an important role in a plant’s life, both good and bad. Some bacteria, such as the ones that cause wilt and rust, may induce diseases in plants. Others, such as the nitrogen-fixing bacteria, may play a vital role in growth and in repairing damage.

Ultraviolet light is detrimental to these microbes and may result in their death. Many scientists have tried using UV light to kill pathogens. The problem is always the same: while ultraviolet light kills off germs, it also destroys beneficial and symbiotic microbes that play an active role in the healthy growth of a plant.

When UV light kills of these organisms, it causes changes in the composition of materials that the plant needs to make its food supply. For example, ultraviolet light can cause retardation in plants, if it kills of nitrogen-fixing bacteria, because it reduces the amount of usable nitrogen.

 

Ultraviolet Light Causes DNA Damage

It has been widely documented, that UV-R light is highly damaging to life forms, especially their DNA, lipids and proteins. When DNA is damaged, genetic material retards and either results in mutation or cell apoptosis, where the cell engulfs itself to protect itself from damage.

DNA damage, however, may not always be a negative; mutations in plants are the evolutionary forces that lead to greater diversity and often stronger organisms more suited to surviving. For example, plants are able to make use of blue light and UV-A to push toward controlled apoptosis. This ensures that nutrients are not wasted and organs that have grown old are eliminated so new organs can be formed.

 

UV Light Leads to UV-Resistant Crops

With the world heading toward a possible climatic crisis, many researchers have started worrying about the impact of UV light on crops. Considering how thin the ozone layer has become, it is highly likely that in the near future, more DNA-damaging UV radiation will make it through the atmosphere down to the earth’s surface.

This does not necessarily have to be bad news, though. In controlled laboratory experiments, researchers found that crops that were exposed to more UV light actually started producing molecules to block it. This means that these crops are able to survive in harsher climates and drier regions. Moreover, the plants then used ultraviolet light to their advantage to curb mold and other diseases that were festering in the soil.

This new research might be critical in the future as global warming raises temperatures, the ozone layer is further depleted and more light penetrates down to the earth’s surface. And, not only did plants become more resistant to harmful light and microbes in those experiments, they also changed their shapes: they became shorter and thicker, which helps reduce water loss.

While UV light is generally harmful to plants, it can still be used to bring about positive effects. A final such effect comes in the growing of cannabis. Ultraviolet light causes the production of resin, and with it THC, in order to protect the marijuana plant from harmful UV rays. Thus, adding UV light to LED grow lights results in an increase in THC in the resulting buds.

There is no question that at its core, UV light is harmful to plants. But in harming plants, it actually causes them to develop protective mechanisms that make them stronger going forward. For this reason, feeding your indoor plants low levels of supplemental UV light will actually help them and generally result in better crops (as is the case with marijuana).

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