Fri, 23 Jul 2010 10:48p.m.
By Fiona Hodge
Think there’s no violence in the plant kingdom? Think again. Recent research has revealed sphagnum mosses have tiny air guns. Even more shocking is that they use these air guns to shoot their spores, their offspring, out into the world.
Physicist Dwight Whitaker and biologist Joan Edwards revealed this parental eviction using high speed, high magnification videos. Their videos showed the sphagnum spores held inside a small ball-shaped capsule on top of the plant.
As the surface cells of the ball-shaped capsule dry out, the ‘skin’ of the capsule contracts. The capsule is forced into a cylindrical shape, elevating the inside pressure to roughly three to five times atmospheric pressure.
After that Whitaker says the capsule “blows it’s top: sort of like a champagne cork shooting up” releasing the spores along with the roof of the capsule.
Whilst all this is amazingly marvellous, it didn’t explain everything: spores were travelling 11 cm into the air, much higher than theoretical physics suggested that the small particles should.
So the scientists slowed the footage down, had a closer look at the spore clouds and spotted an interesting aerodynamic trick which significantly increased the efficiency of spore travel. The spores were travelling in a vortex ring.
A vortex ring is a way for a fluid to move through another. A smoke ring is a great example of one – the smoke being one fluid, the air being the other. The smoke moves as if it is flowing around a doughnut: up through the hole, out over the sprinkles, back down the outer edge, in underneath, and up through the hole again.
In the case of the mosses the spore filled air released from the capsules moves in the same way as the smoke. Whitaker says this type of spore movement is very efficient as the drag on the spores is significantly reduced.
Why does the sphagnum moss need such a fancy offspring launching system? The Achilles heel of all mosses is their lack of internal plumbing, or vascular system. Without plumbing to suck water up from the soil and move it around the plant, these plants need to lay low and stay close to the damp ground.
Being small and wind dispersed is bad news for spore dispersal – particularly as the air close to the ground forms a still boundary layer. Spores that escape this still boundary layer, usually about 10 cm thick, will be dispersed much further in the breezier air above.
Their reward? Our respect. Additionally they’re doing all right in terms of abundance… It’s estimated the 285 species of sphagnum moss cover 1% of the earths land surface.