Redwood leaf discovery surprises scientists
California’s towering redwoods have been around for thousands of years, but the trees are still yielding some surprises about what makes them so resilient.
UC Davis scientists recently discovered that redwoods have two different types of leaves — and those leaves play different roles, but work together to help the trees thrive in both coastal and drier inland areas where they grow.
The trees’ peripheral leaves, like those on most trees, are food producers that convert sunlight into sugar through photosynthesis. But the axial leaves serve an entirely different role, researchers found — absorbing water.
Redwoods, the tallest and among the oldest trees on Earth, grow naturally in both wet coastal areas of California as well as drier mountainous regions. They’re known to grow exclusively in California and southern Oregon, living an average of 500 to 700 years, with some living as long as 2,000 years.
According to the study, published in the American Journal of Botany, a large redwood can absorb 14 gallons of water in just the first hour after its leaves become wet.
The differing roles of the leaves was discovered during a study estimating, for the first time, the amount of water absorbed in the full crown of redwoods.
Researchers collected shoot clusters from six redwood trees at five forest locations reaching from Del Norte County to the Santa Cruz Mountains and exposed them to simulated fog, according to a UC Davis spokesperson. They estimated water absorption for seven other trees — including the tallest living tree — and took samples at varying heights. Then they compared the anatomy and measured photosynthesis of the peripheral and axial leaves to determine their functions.
In some trees, when leaves get wet, they inhibit the photosynthesis process, the study found. But in redwoods, the different leaf types allow photosynthesis to continue — even in the rain and fog.
“Having leaves that aren’t for photosynthesis is in itself surprising,” said Alana Chin, a doctoral student in ecology at UC Davis and lead author of the study. “If you’re a tree, you don’t want to have a leaf that’s not photosynthesizing unless there’s a very good reason for it.”
The study also found that redwoods can change the location of their leaves depending on the climate. Along the west North Coast, water-absorbing leaves are found on the lower branches, leaving the upper branches for the sun-collecting and photosynthesizing leaves. In drier southern areas, the opposite is true with the watergathering leaves near the tops of the trees where they can catch more rain and fog.
Chin, who grew up near redwoods in Mendocino County, said the study is further evidence of the big trees’ ability to adapt to environmental changes — including drought.
“The cool thing here is their ability to thrive under all these circumstances and adjust themselves to these different environments,” Chin said in a news release from the university. “That things like this can be happening right under our nose in one of the best-studied species out there — none of us assumed this would be the story.”