Science Diary: Redwoods – Straw

Music; Ambience: drinking straw sucking water; forest ambience

That’s the sound of water being sucked through an 8-inch drinking straw. Well now, imagine being on a balcony 30 stories high and using a 300-foot straw to drink from a water glass on the ground. Well, giant redwood trees routinely pull groundwater into their 300-foot crowns, and that’s a lot of suction power; so much power, in fact, that it can shut down the growth of a tree. Welcome to Pulse of the Planet’s Science Diaries, a glimpse of the world of science from the inside.

Koch: As trees get taller, they’ve had to pull water further from the source at the ground. And that imposes water stress on the leaves and on the conduits that are moving that water. And it’s imposing restrictions on photosynthesis.

That’s physiologist George Koch, who made this recording high up in the canopy of a California redwood forest, in the company of buzzing insects. As you may remember from school, photosynthesis is the process by which plants turn sunlight into sugar, and carbon dioxide into oxygen. And it’s the engine that drives the growth of a tree. But if the world’s tallest trees overdo the suction, it can actually shut down their growth.

Koch: You know, if you suck super-hard on a weak straw, the straw collapses. And then you can’t pull anything through it anymore. And although the tree’s straws, so to speak, they don’t collapse, they do fail and if there’s enough suction pressure on them, an air bubble can be pulled in, and that blocks the flow of water through those conduits. And that’s one of the problems that we think these tall trees encounter. And the only way to completely avoid that is for the tree to close down the little pores in the leaves that allow water out and carbon dioxide in. They have to limit their photosynthesis. And that may be why these trees grow more slowly as they grow taller.

Pulse of the Planet’s Science Diaries are made possible by the National Science Foundation. I’m Jim Metzner.

Science Diary: Redwoods - Straw

Imagine sucking water through a 300-foot straw; giant redwoods do this, in effect, every day.

Air Date:08/11/2008

Scientist:

Transcript:

Science Diary: Redwoods - Straw

Music; Ambience: drinking straw sucking water; forest ambience

That's the sound of water being sucked through an 8-inch drinking straw. Well now, imagine being on a balcony 30 stories high and using a 300-foot straw to drink from a water glass on the ground. Well, giant redwood trees routinely pull groundwater into their 300-foot crowns, and that's a lot of suction power; so much power, in fact, that it can shut down the growth of a tree. Welcome to Pulse of the Planet's Science Diaries, a glimpse of the world of science from the inside.

Koch: As trees get taller, they've had to pull water further from the source at the ground. And that imposes water stress on the leaves and on the conduits that are moving that water. And it's imposing restrictions on photosynthesis.

That's physiologist George Koch, who made this recording high up in the canopy of a California redwood forest, in the company of buzzing insects. As you may remember from school, photosynthesis is the process by which plants turn sunlight into sugar, and carbon dioxide into oxygen. And it's the engine that drives the growth of a tree. But if the world's tallest trees overdo the suction, it can actually shut down their growth.

Koch: You know, if you suck super-hard on a weak straw, the straw collapses. And then you can't pull anything through it anymore. And although the tree's straws, so to speak, they don't collapse, they do fail and if there's enough suction pressure on them, an air bubble can be pulled in, and that blocks the flow of water through those conduits. And that's one of the problems that we think these tall trees encounter. And the only way to completely avoid that is for the tree to close down the little pores in the leaves that allow water out and carbon dioxide in. They have to limit their photosynthesis. And that may be why these trees grow more slowly as they grow taller.

Pulse of the Planet's Science Diaries are made possible by the National Science Foundation. I'm Jim Metzner.