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  • [INTRO ♪]

  • The South Pacific island of New Caledonia has one of the weirdest plants on Earth.

  • It's a tree whose sap is this teal-ish, blue-green color that you don't usually see in natureespecially not in living things.

  • But as alien as it looks, the green color is totally natural, and it comes from the fact that more than a quarter of the sapis metal.

  • The tree is called Pycnandra acuminata, and it grows in the rainforests in what are called ultramafic soils.

  • Ultramafic soils are sort of unusual because they form from rocks with large concentrations of nickel.

  • And rocks like that are rareyou typically only see them in places where material from the Earth's mantle has been pushed to the surface.

  • In general, that type of soil is also pretty hard for plants to grow in.

  • Even though they need a little bit of nickel to survive, too much of it is typically toxic.

  • That's because nickel has a similar chemical structure to other nutrients plants need to grow, like calcium and magnesium, so plants can end up absorbing nickel instead of some of the other nutrients they need.

  • All that nickel can mess with their metabolism and stunt their growthif it doesn't just straight-up kill them.

  • But the roots of Pycnandra acuminata guzzle up that metal, and the plant has about 250 grams of nickel per kilogram of sap.

  • That's around 250 thousand times more than your average plant.

  • It also happens to be enough to turn its sap green.

  • But this tree doesn't seem to mind.

  • That makes it a metal hyperaccumulatorin other words, a plant that can deal with a lot of metal.

  • These plants deal with nickel by capturing it with molecules called ligands, which bind to nickel atoms and prevent them from reacting with other chemicals.

  • That helps keep the plant's chemical structure intact despite all that extra metal.

  • Pycnandra acuminata also basically quarantines the nickel in cells that are separate from other parts of the plant.

  • And those solutions seem to work out for this tree.

  • The question is why plants like these have evolved to store so much metal, and scientists haven't figured out the exact reason.

  • One possibility is that it evolved as a way of surviving extremely metallic soils.

  • But scientists think it's now what's called an exaptation—a trait evolved for one purpose but now serves a different one.

  • For example, one hypothesis suggests that plants build up all this nickel to protect themselves from predators, since nickel is toxic to animals as well plants.

  • But the case isn't closed.

  • While there's evidence that some insects are sensitive to high levels of nickel in plants, larger plant-eaters don't seem to be put off by it at all.

  • So there may be a different reason plants have this trait, and another hypothesis suggests that the nickel is a type of chemical attack on other plantssomething called allelopathy.

  • The idea is that when a hyperaccumulator's leaves drop to the ground, they enrich the nickel in the soil and make it harder for other plants to thrive.

  • Its young offshoots may have a better chance of surviving if they don't have to compete with other plants for resources.

  • But while there's some evidence for it, this idea isn't proven yet either.

  • Whatever its reason for being the way it is, this bizarre tree could offer us more than its weirdness.

  • Metal hyperaccumulators like it could make it possible to remove metal pollutants from soils, which could be valuable here on Earth or even in future civilizations on Mars.

  • But we have to protect this tree because there are only a few hundred left, and we still have plenty more to learn from it.

  • [OUTRO ♪]


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