As the global climate changes, plants and animals have adapted by expanding into new territories and even shifting breeding seasons.
Now, research suggests that over the past 75 years, flowers have also adapted to rising temperatures and lowering ozone by altering the ultraviolet (UV) pigments in their petals.
The UV pigments of flowers are invisible to the human eye, but they attract pollinators and serve as a kind of sunscreen for plants, says Matthew Koski, a plant ecologist at Clemson University.
Just as ultraviolet radiation can be harmful to humans, it can also affect the pollen of a flower. The more pigments the UV-absorbing pigment contains, the less harmful the radiation reaches sensitive cells.
Earlier, Koski and colleagues found that flowers exposed to more UV radiation – usually those that grow at higher altitudes or closer to the equator – had more UV pigment in their petals.
It was then asked whether the deterioration of the ozone layer and the temperature changes influenced the UV pigments.
And to find out, Koski and his colleagues examined plant collections from North America, Europe and Australia, dating from 1941.
In total, they examined 1238 flowers from 42 different species. They photographed flower petals of the same species collected at different times along their natural area using an ultraviolet-sensitive camera, which captured changes in the UV pigment. They then adapted these changes to local ozone level and temperature data.
The results show major changes in the landscape
On average, the pigment in flowers in all locations has increased over time with an average of 2% per year from 1941 to 2017.
But the changes also varied depending on the structure of the flower. In large, plate-like flowers with exposed pollen, the UV-absorbing pigment increased when ozone levels dropped and fell in places where ozone rose.
But flowers with pollen hidden in their petals have reduced their UV pigment as temperatures have risen, regardless of whether ozone levels have changed.
While it may be surprising, the finding “makes perfect sense,” says Charles Davis, a plant biologist at Harvard University who was not involved in the paper.
Although such changes in the pigment cannot be distinguished from the human eye, they stand out and function as a beacon for pollinators such as hummingbirds and bees.
Koski says that most pollinators prefer flowers with a “bull’s eye” pattern: the tips of the petals that reflect UV and the pigments that absorb UV near the center of the flower.
As a result, these changes in the pigment can help protect pollen, but pollinators will remain inactive, and the repercussions can be serious for humanity in terms of food shortages.