Natures wonders: how redwoods adapt for water (Introduction)

by David Turell , Sunday, April 17, 2022, 15:48 (739 days ago) @ David Turell

They are giants, live in California with low rainfall, and have special adaptations of their leaves:

https://www.sciencealert.com/redwood-trees-have-a-secret-trait-that-helps-them-fight-cl...

"Because redwoods are long-lived, large, and decay-resistant, the forests they dominate store more above-ground mass, and thus presumably more carbon, than any other ecosystem on Earth.

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"Redwoods, it turns out, have two types of leaves that look different and perform very different tasks. This previously unknown feature helps the trees adapt to both wet and dry conditions – an ability that could be key to their survival in a changing climate.

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"Scientists have long known about redwoods' ability to absorb water through their leaves. But figuring out how much water redwoods can absorb this way, and how the capacity to do so might vary from one type of climate to another, is a real challenge in this species.

"First, a big redwood has over 100 million leaves with a massive amount of surface area for water absorption. And these leaves drastically change structure with height, going from long and flat to short and awllike. So we couldn't get this right by simply picking leaves at ground level.

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"To complicate matters further, gravity is always pushing down on the giant column of water rising upward through a redwood's trunk. As a result, leaves at the top of the tree always have less available water than those lower down.

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"As we took apart clusters of redwood shoots to immerse them in fog, we divided each cluster into pieces. Redwood shoot clusters fan out from a woody core and are segmented into individual shoots of multiple ages, each with its own set of leaves. We separated shoots along the woody central axis from the much more common pliable shoots on the outer edges of each cluster.

"It quickly became obvious that shoots from the center axis had leaves that could absorb water three times faster than peripheral leaves. When we looked inside the leaves with a microscope, we understood that they were two completely different types.

"They don't look the same on the outside either, but this was so unexpected that we needed to see their internal structure to really convince ourselves.

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"With some additional measurements, we found that redwoods' axial leaves are specialized for absorbing water. Differences between the surfaces of axial and peripheral leaves, especially their wax coverage, cause the differences in their water absorption rates.

"Unlike the axial leaves, redwoods' peripheral leaves have waxy surfaces with lots of stomata. This helped to explain how they photosynthesize year-round regardless of the long wet season in much of their current habitat.

"Further analysis showed that the redwoods' axial leaves account for only about 5 percent of the trees' total leaf area, and barely produce enough energy through photosynthesis to maintain themselves. But they contribute up to 30 percent of the trees' total water absorption capacity.

"Together these two types of leaves balance the dueling requirements of photosynthesis and water absorption, allowing redwoods to thrive in both wet and dry habitats.

"Using large-scale tree measurements and equations for estimating redwood leaf area, we estimated that these thirsty giants can absorb as much as 105 pounds (48 kilograms) of water in the first hour of a rainfall wetting their leaves. That's equivalent to 101 pints of beer.

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"Redwoods vary their two leaf types to suit their local climates. In wet rainforests in the northern part of their range, above Mendocino County, the trees invest in fewer of the axial leaves that are specialized for absorbing water.

"These leaves are concentrated in the trees' lower crowns, leaving the photosynthetically high-performing treetops free to maximize sugar production in the bright sun.

"In dry forests on the southern margins of redwoods' range, trees have more axial leaves in their water-stressed tops.

"This allows them to take better advantage of briefer leaf-wetting events, but it means they photosynthesize less per leaf area than redwoods in wetter areas.

"Redwoods' ability to shift leaf types to match regional climatic differences may help them adjust to climate change in an ever-drier California."

Comment: dhw will wonder why these trees exist. I accept they do.