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0:00We can hardly believe it: we’ve
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0:20One of them is not like the others…
0:25Trees are the heaviest and
largest living things on Earth,
0:28with the most massive tree weighing almost
2,000 tons – as much as ten blue whales.
0:35But instead of floating weightlessly in the
ocean it reaches 25 stories into the sky,
0:40held in place by surprisingly shallow roots.
0:44You’d think trees grow from the ground because,
0:46well, they are made of stuff and there is
stuff in the ground – but if something so
0:50massive and huge ate something down
below, it would have to leave holes.
0:54Instead trees are growing by
literally eating thin air!
0:59But this is only half of the
story because down in the ground,
1:02roots are mining rocks in ways
weirder than you can imagine.
1:08How to Eat Air to Grow Huge
1:11Carbon is the most valuable
material for living things.
1:15A chemical multi tool you can
make almost everything from – and
1:18a good amount of it just floats
around in the air and the oceans.
1:22What makes plants so incredibly
successful is that over a billion
1:26years ago their ancestors became better than
any other living thing at harvesting carbon.
1:32They used it to grow and grow and grow.
1:35Today plants make up 80% of the biomass
on earth and are the basis for all complex
1:40life – all animals eat either plants or animals
that eat plants, to get the carbon they need.
1:47Trees are an especially ingenious way plants
found to harvest massive amounts of carbon.
1:53Trees are big and heavy and so
they need a lot of material.
1:57But the atmosphere is only about 0.04% CO₂.
2:01425 CO₂ molecules per
million molecules in the air.
2:06To get a single tonne of carbon
a tree has to process 6000 tons,
2:11or 5 million cubic meters of air!
2:16So trees developed sophisticated biological
industrial megalopolises: Their crowns.
2:22A huge industrial park network, made from
dozens of branches, subbranches and hundreds
2:28of thousands of twigs that can sense the sun and
shape the tree to grow towards it in slow motion.
2:35They are carrying up to a million leaves, the
industrial parks where a tree eats and builds,
2:40consuming extreme amounts of resources
from the air and fed by the roots
2:44down below while vomiting waste and
changing the climate around them.
2:49Let’s zoom into a single leaf.
2:52It is made from hundreds of millions of
factory cells and optimized to have as
2:56much surface area and be as thin
as possible to harvest sunlight.
3:01While your skin is hundreds of cells thick,
a leaf can be just ten cells top to bottom.
3:06On their top leaves have only a single,
3:09ultra thin layer of protective transparent “skin”
cells that let light through and keep water in.
3:15Below them are layers of factory cells, filled to
3:18the brink with chloroplasts
that do the actual work.
3:21Beneath them a spongy layer of loose
cells enables gases to travel around.
3:26The whole leaf is traversed by a
network of vein-like superhighways,
3:30that carry sugars back down and bring
water and minerals up from the roots.
3:35At the bottom is another protective layer of
cells interrupted by hundreds of thousands
3:40of stomata – tiny mouths opened and closed by
two guard cells that look a bit like lips.
3:46Each day an adult tree pulls up
dozens of liters of water all the
3:50way from its roots in the ground to these veins,
3:52where about 95% of it is sweated out through
hundreds of billions of these tiny mouths.
3:57This cools the leaf factories, which
need to stay in direct sunlight as
4:01long as possible, and the air around the tree.
4:04And it surrounds the tree with an invisible mist.
4:07The vapor from a forest of billions of
trees can seed clouds and create rain.
4:13Rainforest is literal – without the trees the
amazon would be a sad dry shrubland or desert.
4:20The other 5% of the water is used to
keep the cells alive and to power the
4:25factories where the magic happens: Photosynthesis.
4:28We are not going to explain the
details here, but in a nutshell,
4:31with the energy from the sun, water
molecules are split into hydrogen and oxygen.
4:36The oxygen is ejected, while the
leftover hydrogen and CO2 are forged
4:41and reduced into glucose – a simple sugar
that’s both battery and building block.
4:47And the source of most carbon
in the world for most animals.
4:51Oxygen is not just garbage to the tree though.
4:55To actually use the energy stored in the
glucose, the tree has to burn the sugar,
4:59just like we humans do, with cellular respiration.
5:02So all living cells in the tree suck in
oxygen – through the tiny leaf mouths,
5:07cracks in the bark, and even root tips tapping
into tiny air pockets hidden in the soil.
5:13This respiration runs nonstop, and especially at
night when the leaf factories stop production.
5:20Trees actually reabsorb some of the
oxygen they produce and almost all
5:24of the rest gets used up by microbes
and everything else breathing nearby.
5:28Most of the world's free oxygen doesn't come
5:31from trees but from algae and
cyanobacteria in the oceans.
5:35But this is only half of the story
because the even more insane parts of
5:39trees are the second invisible crown:
the underground empire of the roots.
5:45Most of the water a tree needs comes from rainfall,
which soaks mainly into the upper layers of soil.
5:51Annoyingly for trees their
crowns are big umbrellas,
5:54so their roots need to spread out
far and wide towards the side.
5:58About 50% of their roots are packed
into the top 25 centimeters of soil.
6:03They are not a mirror image of the
crown, but a dense, tangled mat,
6:06deeply intermingled with their neighbours’.
6:09Only if it’s very dry do roots grow
straight down to tap hidden water reserves,
6:13in extreme cases more than 20 stories deep.
6:17But this is a rare exception.
6:18Most roots reach down 7m.
6:21But roots have a far more complex
job than just catching water.
6:25Just like you can’t build a city from
only bricks and steel, trees also need
6:29some rare materials: phosphorus to build
DNA, nitrogen for proteins and many more.
6:35And all of these are
stealthily buried underground.
6:38Rocks, dry patches, nutrients, and rival roots
are all scattered unpredictably and chaotically.
6:44To navigate this shifting maze,
6:46roots evolved a specialized sensor
at their very tip: the root cap.
6:51Each cap is filled with gravity-sensing cells,
6:54in which tiny dense particles sink like
pebbles settling in a jar of water.
6:59So the root always knows which way is down.
7:01As it pushes forward, specialized
cells detect moisture, temperature,
7:06chemical gradients and the
smallest vibrations from water.
7:10This raw data flows into the root’s
command center just behind the tip,
7:14where cells produce electrical pulses
and move transmitter chemicals around.
7:18Signals from the soil are processed, interpreted
and turned into decisions about where to grow.
7:24A single tree has hundreds of thousands of these
7:27command centers and they seem to
share information with each other.
7:31Once a root has chosen a path, fuzzy
little drinking straws called root hairs,
7:35loaded with enzymes and transport proteins,
begin soaking up water and dissolved minerals.
7:41But many essential nutrients
are locked away in solid rock.
7:45So roots evolved to move into the finest cracks.
7:48Once in, they fill with water and
swell like tiny hydraulic jacks,
7:53creating enough pressure to
break even the hardest rock.
7:56Next they release a mix of acids
that seep into the fractures and
8:00dissolve the bonds that hold nutrients in place.
8:03Claw-like molecules grab them and pull
them in before they can slip away.
8:07This sophistication really is
stunning but it gets even wilder.
8:12Even with all these tools, to really
thrive, the tree needs allies.
8:16And it found them: fungi.
8:20The underground networks of
fungi can stretch for kilometers.
8:23They are so small that they
can go where roots can’t,
8:26slipping between grains of soil to
reach distant pockets of nutrients.
8:32So hundreds of millions of years ago
roots and fungi formed a trade alliance.
8:37The trees provide a cut of the sugars they
produce far up in the sky and fungi collect
8:42and give them nutrients and water in return.
Some fungi grow directly into the root’s cells,
8:49building tiny trade posts, where
sugars and minerals change hands.
8:53Others wrap themselves around root
tips, weaving between their outer
8:57layers, insulating delicate tissues and
protecting them against microorganisms.
9:02Today there are thousands of fungal tree
ally species, each with its own specialties.
9:08Some only partner with specific tree species,
while others are happy to work with almost anyone.
9:14These connections often knit the roots of many
trees together into vast underground networks.
9:20Their scale is gigantic.
9:22In just one cubic meter of healthy forest floor,
fine tree roots can stretch for several kilometers
9:27and for every kilometer of root, there can
be hundreds of kilometers of fungal networks.
9:33It’s one of the largest and most
intricate living structures on Earth,
9:37and may even connect whole forests.
9:41We are only beginning to understand how complex
and intricate the relationships between trees,
9:46their offspring, relatives and rivals,
microbes and fungal networks are.
9:51But the more we’ve learned
over the last few decades,
9:54the clearer one thing has become:
Trees are just so incredibly wild.
10:00And we have so much more to learn.
10:05People once believed that all fungi — even those
allied with trees — were just strange plants.
10:10But then, some incredible
minds discovered that they
10:13were actually an entirely different life form!
10:16This breakthrough in understanding
was powered by a combination of
10:19technical knowledge and problem-solving skills.
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