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Ancient redwoods recover from fire by sprouting 1000-year-old buds

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When lightning ignited fires around California’s Big Basin Redwoods State Park north of Santa Cruz in August 2020, the blaze spread quickly. Redwoods naturally resist burning, but this time flames shot through the canopies of 100-meter-tall trees, incinerating the needles. “It was shocking,” says Drew Peltier, a tree ecophysiologist at Northern Arizona University. “It really seemed like most of the trees were going to die.”

Yet many of them lived. In a paper published yesterday in Nature Plants, Peltier and his colleagues help explain why: The charred survivors, despite being defoliated [aka losing all their needles], mobilized long-held energy reserves—sugars that had been made from sunlight decades earlier—and poured them into buds that had been lying dormant under the bark for centuries.

“This is one of those papers that challenges our previous knowledge on tree growth,” says Adrian Rocha, an ecosystem ecologist at the University of Notre Dame. “It is amazing to learn that carbon taken up decades ago can be used to sustain its growth into the future.” The findings suggest redwoods have the tools to cope with catastrophic fires driven by climate change, Rocha says. Still, it’s unclear whether the trees could withstand the regular infernos that might occur under a warmer climate regime.

Mild fires strike coastal redwood forests about every decade. The giant trees resist burning thanks to the bark, up to about 30 centimeters thick at the base, which contains tannic acids that retard flames. Their branches and needles are normally beyond the reach of flames that consume vegetation on the ground. But the fire in 2020 was so intense that even the uppermost branches of many trees burned and their ability to photosynthesize went up in smoke along with their pine needles.

Trees photosynthesize to create sugars and other carbohydrates, which provide the energy they need to grow and repair tissue. Trees do store some of this energy, which they can call on during a drought or after a fire. Still, scientists weren’t sure these reserves would prove enough for the burned trees of Big Basin.

Visiting the forest a few months after the fire, Peltier and his colleagues found fresh growth emerging from blackened trunks. They knew that shorter lived trees can store sugars for several years. Because redwoods can live for more than 2000 years, the researchers wondered whether the trees were drawing on much older energy reserves to grow the sprouts.

Average age is only part of the story. The mix of carbohydrates also contained some carbon that was much older. The way trees store their sugar is like refueling a car, Peltier says. Most of the gasoline was added recently, but the tank never runs completely dry and so a few molecules from the very first fill-up remain. Based on the age and mass of the trees and their normal rate of photosynthesis, Peltier calculated that the redwoods were calling on carbohydrates photosynthesized nearly 6 decades ago—several hundred kilograms’ worth—to help the sprouts grow. “They allow these trees to be really fire-resilient because they have this big pool of old reserves to draw on,” Peltier says.

It's not just the energy reserves that are old. The sprouts were emerging from buds that began forming centuries ago. Redwoods and other tree species create budlike tissue that remains under the bark. Scientists can trace the paths of these buds, like a worm burrowing outward. In samples taken from a large redwood that had fallen after the fire, Peltier and colleagues found that many of the buds, some of which had sprouted, extended back as much as 1000 years. “That was really surprising for me,” Peltier says. “As far as I know, these are the oldest ones that have been documented.”

... “The fact that the reserves used are so old indicates that they took a long time to build up,” says Susan Trumbore, a radiocarbon expert at the Max Planck Institute for Biogeochemistry. “Redwoods are majestic organisms. One cannot help rooting for those resprouts to keep them alive in decades to come.”

-via Science, December 1, 2023

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Not a Plant, Not a Sheep… It's a Photosynthesizing Slug!

But it’s dressed like a plant… and powers itself like one, too.

Meet the Leaf Sheep (Costasiella kuroshimae) — one of the smallest and strangest marvels of the sea.

Barely the size of a grain of rice, this creature has black ear-like tentacles, bead-black eyes, and a back covered in tiny green “leaves.”

Those aren’t leaves at all — they’re cerata, filled with stolen chloroplasts from the algae it eats.

Through a process called kleptoplasty, the Leaf Sheep turns sunlight into energy, making it one of the few animals on Earth to photosynthesize.

Its leafy camouflage hides it among seaweed while its stolen solar cells fuel its day.

Drifting through warm Indo-Pacific reefs, it grazes on algae like a tiny sheep of the sea… except this one runs on sunlight.

Elysia viridis: this sea slug is one of the few known animals that can engage in photosynthesis, which allows it to survive without food for months at a time

Elysia viridis is a sacoglossan sea slug with an unusual ability -- it can "steal" the photosynthesizing organelles from algae and then incorporate those chloroplasts into its own body, where they continue to convert sunlight into energy. This process produces nutrients that supplement the sea slug's diet.

Above: Elysia viridis

The acquired chloroplasts are often referred to as kleptoplasts, which means "stolen plastids." Their photosynthesizing ability allows the sea slug to survive with limited food (or no food at all) for months at a time.

As this article explains:

In sacoglossan sea slugs, kleptoplasts are harboured in cells of the digestive diverticula, enabling their animal host to survive photo-autotrophically for periods ranging from days to up to one year after being "stolen" from algal cells.

Due to these remarkable features, sacoglossan sea slugs have frequently been termed "leaves that crawl" or "solar-powered sea slugs."

Elysia viridis can have a green or reddish-brown appearance, depending on the amount of light that it receives and the color of the algae that it consumes. Its body is also covered in glittering, iridescent flecks of blue and green.

Above: the photo at the top shows Elysia viridis with its parapodial lobes folded over its body, while the photo at the bottom shows the same species with the lobes completely unfurled

The sea slug's body is flanked by two flat, wing-like lobes that can fold inward or unfurl, allowing the animal to regulate its light exposure. When these flaps are stretched open, the sea slug looks remarkably similar to a leaf; its body has a flat, wavy appearance, and its digestive glands are clearly visible just beneath the surface of the skin, mimicking the veins of a leaf.

Above: Elysia viridis as a baby

Several other sea slugs are also known to engage in photosynthesis, but this phenomenon is still remarkably rare among animals at large. Most of the animals that do photosynthesize are marine invertebrates, including sacoglossan sea slugs and certain nudibranchs.