Thomas Forrest March 1, Takeaway: While getting your tan on is a favorite holiday pastime, we often forget the nasty consequences of too much sunlight on our skin. UV light is harmful to plant tissue too, but research shows that it can also benefit our little green friends.
But, how have our floral friends evolved to deal with this UV light energy? Well, UV radiation can be harmful to plant tissue too, but modern research is proving there are also several distinctly positive responses to UV radiation. What is UV light?
Ultraviolet light is an electromagnetic radiation with a wavelength from nanometers nm. This is a shorter wavelength than visible light but longer than X-rays. Email Newsletter Join thousands of other growers who are already receiving our monthly newsletter. This radiation can be broken down into three bands: These radiations propagate only in a vacuum.
How does UV light affect plants? As sunlight shines down upon a crop, plants expose the surface of their leaves to capture solar rays. While some of this light energy is used in photosynthesis, some of it regulates different developmental processes—such as advancing growth in good conditions or causing deviations for survival during periods of stress—to optimize the photosynthetic processes and detect seasonal changes.
This light-mediated development of form and structure is known as photomorphogenesis. Photoreceptors are also sensitive to light quantity, quality, and duration. For example, plants growing beneath the canopy use phytochromes to sense the reduced amount of light reaching the plant and regulate such processes as shade-avoidance, competitive interactions, and seed germination.
However, it is extremely difficult for scientists to match specific responses to individual photoreceptors. Typically, multiple photoreceptors will interact to produce a single change. Also, some photoreceptors like phytochromes are sensitive to more than one light wavelength. Phytochromes, which mediate many aspects of vegetative and reproductive development, are responsible for absorbing red and far-red light but also absorb some blue light and UVA radiation. On the Dawn of a Grow Light Revolution: How Plants Use Different Wavelengths for more information on this.
When it comes to UV radiation, there are several other photoreceptors responsible for absorbing those wavelengths. It has been proven that UV light influences photomorphogenic responses including gene regulation, flavonoid biosynthesis, leaf and epidermal cell expansion, stomatal density, and increased photosynthetic efficiency. For example, numerous agricultural crops can synthesize simple phenolic compounds and flavonoids that act as sunscreens and remove damaging oxidants and free radicals.
In certain crop species, these phenolic compounds can be extremely desirable and it can be beneficial to the farmer to enhance this aspect of production.
How can growers use UV energy without causing damage to their crops? Although this is a fairly recent field of botanical science, there are reports of dramatic increases in essential oil production by flowering crops grown under lightbulbs with higher UV output.
High UV bulbs are generally recommended for use in the last two weeks of a flowering cycle once the generative development is completely established. This allows for a crop to continually develop in size and growth vigor while also protecting the flowers and canopy with increased resin production. Like all aspects of horticulture, balance is the key to effective UV use.
Timing is also an important part of UV application. When given UVB throughout the entire growth cycle, sensitive plants such as leafy greens often display reduced growth plant height, dry weight, leaf area, etc. Generally, the effectiveness of UVB also varies both among species and among individual strains or genetics of a given species. If we use this technology correctly, we can enjoy the delicious benefits of plant sunscreen.
This means your flowers will smell better, your fruit will taste superior, and your herbs will have a higher potency in the kitchen. Written by Thomas Forrest After being introduced to aquaponics five years ago, Thomas Forrest quickly became an enthusiastic gardener. Following his university studies in business and media, Thomas completed his Production Horticulture Certificate at the National Precision Growing Centre. He is a sales rep for Stealth Garden Supplies in Australia.