DISCOVERY: Redwoods use two completely different types of leaves to manage sunlight and water use, say UC Davis and Cal Poly Humboldt scientists | Lost Coast Outpost



Peripheral (left) and axial (right) redwood leaves. | Photos courtesy of UC Davis

California’s coast redwoods are even better suited to local climates than scientists previously thought, according to a new study published in the American Journal of Botany.

The study, authored by researchers at UC Davis and Cal Poly Humboldt, shows that redwoods use two different types of leaves to manage their sun and water intake.

“Redwoods are among the most studied trees on the planet, yet their mysteries continue to surprise and delight scientists and nature lovers alike,” UC Davis said in a March press release.

While peripheral redwood leaves function like most tree leaves, converting sunlight into sugar (tree food) through photosynthesis, axial redwood leaves would have an entirely different purpose. According to the study, these axial leaves are almost exclusively dedicated to water absorption and contribute very little to photosynthesis. The tree’s axial leaves are so efficient at absorbing moisture that a large redwood tree with 100 million leaves can absorb up to 14 gallons of water in an hour.

“I’d be surprised if there weren’t a lot of conifers doing this,” said study lead author Alana Chin, a Mendocino County native. “Having leaves that are not intended for photosynthesis is in itself surprising. If you’re a tree, you don’t want to have a leaf that doesn’t photosynthesize unless there’s a really good reason for it.

This leaf variation was discovered while researchers were conducting a first-of-its-kind study that estimated how much water a mature redwood tree could absorb through its crown. The redwood shoot clusters used in the study were collected from six redwood trees in five forest areas between Del Norte County and the Santa Cruz Mountains.

Researchers say the double-leaf system may help redwoods in the process of photosynthesis. While some tree leaves can be flooded with excess water during the rainy season, limiting their potential to absorb sunlight, peripheral redwood leaves have a waxy coating, which slows absorption. of water and can help trees photosynthesize all year round.



Wax on the surface of redwood leaves.

The study also found that redwoods have the ability to alter the placement of these types of leaves, allowing the trees to thrive in both wet and dry regions of northern California and southern Oregon. For example: in temperate rainforests, peripheral sun-absorbing leaves are found in the upper branches of redwood and axial water-absorbing leaves are found in lower branches – a strategy that allows trees to absorb more of sunlight. In drier regions, the researchers found the opposite: water-absorbing leaves in the upper branches and photosynthetic leaves below. The study suggests this allows the trees to collect more rainwater and fog.

“What’s cool here is their ability to thrive in all of these circumstances and adapt to these different environments,” Chin said. “That things like this could happen right under our noses in one of the best-studied species – none of us thought that would be history.”

Cal Poly Humboldt professors Stephen Sillett and Lucy Kerhoulas and the university’s College of Natural Resources and Science equipment technician Marty Reed co-authored the study.



Lead study author Alana Chin.

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