New research suggests that over the past three-quarters of the century, flowers have begun adapting to rising temperatures and declining levels of ozone in the atmosphere, by altering ultraviolet (UV) pigments in their petals.
Published in Current Biologylast week, the study analyzed plant collections from North America, Europe, and Australia dating back to 1941, and comprising 1,238 flowers from 42 different species. In a bid to examine variations in levels of UV-pigmentation of the flowers over time, the researchers photographed their petals using UV-sensitive cameras to capture changes in UV pigment, and also relied on herbarium records, or preserved specimens of flowers. Upon comparison, the results showed that across locations, on an average, UV-pigmentation in flowers increased at a rate of 2% per year from 1941 to 2017.
Having noted the increase in pigmentation over a course of 77 years, the researchers began mapping the changes of individual species to data on their local temperatures and ozone levels. They found that changes in UV-pigmentation of the petals varied depending how the flower was structured. In flowers with exposed pollen, the UV-absorbing pigment increased when ozone levels depleted, but decreased in locations where ozone levels rose.
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But flowers that were structured to enclose pollen within their petals, witnessed a dip in the UV-absorbing pigment, irrespective of changes in ozone levels. “[This] makes total sense,” according to Charles Davis, a plant biologist at Harvard University who was not involved in the study. He explained that although certain flowers that enclose pollen within their petals do get shielded from over-exposure to UV radiation, the enclosure itself can also act like a greenhouse by trapping heat. And, as temperatures rise, so does the greenhouse effect within these flowers, endangering the pollen inside. So, by reducing their UV-absorbing pigmentation, the flowers are attempting to trap less heat, and maintain a cooler temperature for the pollen inside.
However, researchers are worried that this global change in UV-pigmentation may affect the reproductive fitness of plants, due to its repercussions on pollination — a process where floral color plays an important role. While the UV-pigmentation of petals is invisible to the human eye, it attracts pollinators like bees and hummingbirds. Experts believe that lighter color for petals, and a darker centre of the flower, attracts pollinators — with the contrasting hues standing out as a beacon. So, flowers whose petals are witnessing a rise in their UV-pigmentation may become less attractive to pollinators, according to Matthew Koski, the lead researcher of the study. And, as Davis adds, this could even lead pollinators to “miss the flowers entirely.”
According to the UN, 75 percent of the world’s food-crops depend, at least in part, on pollination. But, with air pollution already leading to declining health of wild pollinators, this newly observed effect of climate change on flowers, certainly doesn’t bode well for the future of pollination, and by extension, our food security.
