Thanks to Brilliant for supporting this episode of SciShow. Go to Brilliant.org/SciShow to learn how you can take your chemistry skills to the next level this year! {♫Intro♫} Fish-eating trees sound like they’re straight
out of science fiction. But they’re a real thing—one that exists
right here on Earth. In many forests on the west coast of North
America, the trees eat salmon. And they show just how interconnected life
on this planet is. Now, when we say they “eat” fish, we don’t
mean they’ve developed a mouth full of pointy teeth or razor-sharp claws to pluck a swimming
salmon from the water. What we mean is that the trees obtain a large
portion of their nutrients from fish. And they can do that because bears that do
have pointy teeth and sharp claws catch the fish for them! When salmon are ready to spawn, they make
a one-way trip from the ocean up into streams to lay their eggs. This is an all you can eat buffet for bears
that feast on the salmon to get ready for their long winter hibernation. But bears are messy eaters. For example, in two months, on a single stream,
they left over 5000 kg of salmon scraps along the river banks and into the trees! And those scraps have a lot of something trees
need desperately: nitrogen. Like any living thing, plants need a bunch
of different nutrients to grow. But whichever one is in short supply in a
given area is deemed the limiting nutrient. And along the northwest coast of North America,
the limiting nutrient is often nitrogen. Since fish carcasses have lots of nitrogen
in them, scientists studying these ecosystems suspected the trees were “eating” the
bears’ leftovers, once the salmon decomposed and their nutrients sank into the soil. But to prove it, they needed to follow the
nitrogen! See, not all nitrogen is the same. Some nitrogen atoms have more neutrons than
others. And it turns out nitrogen atoms can have either
seven or eight neutrons and remain stable—so nitrogen has what chemists call two stable
isotopes. Over 99% of the nitrogen on Earth is the lighter
kind: nitrogen-14. But salmon have a weirdly high amount of nitrogen-15,
when compared with land-dwelling species. That’s partly because most salmon spend
nearly all of their adult life in the ocean, and it just so happens that the chemical and
biological processes that occur in seawater make more nitrogen-15 available there than
on land. On top of that, though you may not think of
salmon as fierce predators, they’re actually pretty high up the food chain. And animals use each nitrogen isotope slightly
differently. Because of quirks of biochemistry we don’t
fully understand, nitrogen-14 tends to be excreted more than nitrogen-15. And since this happens at every level of the
food chain, the higher up animals are, the more nitrogen-15 they have in their diet — and
therefore, in their bodies. Starting in the late 1990s, research revealed
that trees near salmon streams in Alaska have impressively high levels of nitrogen-15. The obvious conclusion: they get a lot of
their nutrients from salmon! That wasn’t all. By looking at nitrogen in individual tree
rings—those yearly layers you can see if you cut a tree in half — the researchers
were able to show how important salmon are to the trees. During and after years when more fish came
upstream to spawn, the trees grew bigger rings with more nitrogen in them. And overall, trees that received nutrients
from salmon grew 19% bigger than those that didn’t! So, if you’re a tree who wants to grow nice
and tall, you’d better not skip out on the sushi. And if you’re a human who’s been inspired
by this episode to dive deeper into biochemistry, well, that’s something today’s sponsor—Brilliant.org—can
help with. for example, You could take their course on
chemical reactions and learn about molecules and how they interact. And it’s just one of the fun, interactive
courses you can take with a Premium subscription. And the first 200 people to sign up at Brilliant.org/SciShow
will get 20% off the annual Premium subscription. {♫Outro♫}
