Fall is here and across the country, leaves are turning their traditional autumn colors. And as always, the sight of so many trees decked out in brilliant reds, yellows, and golds, prompts leaf-peepers, kindergarteners, and even scientists to ponder—how come they do that?
After all, it takes energy to produce all those pretty pigments. So why would a tree bother to do it, if those leaves are only gonna turn brown and fall off, anyway?
Now, scientists at the University of North Carolina think they know the dirty secret: it’s the soil. Surveying the sweetgum and maple trees in a nature preserve in Charlotte, the North Carolina researchers found that trees that grew in nutrient-poor soil produced more red pigment, results they just presented at the annual meeting of the Geological Society of America.
Their findings back a discovery made in 2003, by a researcher in Montana, who found that blocking the production of red pigments, in plants that like to make them, renders their leaves unusually sensitive to sunlight. These super-sensitive leaves deliver fewer nutrients to the plant.
So when the soil is poor, it would make sense to make pigment, to keep those leaves working longer. Which is good for the trees—and for the peepers.