As the global climate changes, flowers and animals have adapted, occupied new territories, and even changed breeding seasons. Now, research suggests that over the past 75 years, flowers have also adapted to rising temperatures and ozone depletion by changing the ultraviolet (UV) pigments in their petals.
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Flowers’ The UV pigments are invisible to the human eye, but they attract pollinators and act as a kind of sunscreen for plants, says Matthew Koski, a plant ecologist at Clemson University. Just as UV rays can be harmful to humans, they can also damage pollen. The more UV-absorbing pigments the flakes contain, the less harmful radiation reaches sensitive cells.
Previously, Koski and his colleagues found that flowers exposed to the strongest UV radiation, typically those growing at higher elevations or closer to the equator, had more UV pigments in their petals. He then wondered if two human-influenced factors, ozone depletion and sudden temperature changes, also affect UV pigments.
To find out, Koski and his colleagues had been examining plant collections from North America, Europe and Australia since 1941. In total, they examined 1,238 flowers from 42 different species. They photographed petals of the same species, collected at different times in their natural range, with a UV-sensitive camera that recorded changes in UV pigment.They then compared these changes to local ozone and temperature data.
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On average, flower pigments at all sites increased over time — an average of 2 percent per year from 1941 to 2017, they reported this month in Current Biology. But the changes varied depending on the structure of the flower. In cupped flowers with exposed pollen, such as buttercups, the UV absorbing pigment increases as ozone levels decrease and decreases as ozone levels increase. But flowers with pollen hidden in their petals, like hosepipe, decreased their UV pigment as temperatures rose, whether or not ozone levels changed.
Although surprising, the discovery “makes sense”; says Charles Davis, a plant biologist at Harvard University who was not involved in the work. The pollen hidden in the petals is naturally protected from UV rays, but this extra cover can also act as a greenhouse, locking in heat. He says that when these flowers exposed to hotter temperatures, their pollen can become cooked. Reducing the UV pigments in the flakes allows them to absorb less solar radiation, reducing the temperature.
Although these pigment changes may be indistinguishable to the human eye, they are noticeable to pollinating insects such as hummingbirds and bees. Koski says most pollinators prefer flowers with a “bull’s eyeball”. Design: UV reflecting flower tips and UV absorbing pigments near the center of the flower. Although scientists don’t fully understand the appeal of this pattern, they believe it may help distinguish UV-absorbing background flowers from other plants.