Using High-Speed Video, Prof. Dwight Whitaker and Co-Author Discover a Plant That Produces Mushroom Clouds for Spore Dispersal
Sequential still frames from a video filmed at 10,000fps. Each frame is 1/10,000 of a second. The mushroom cloud with a trailing wake is clearly visible. Photo series by Clara Hard, Joan Edwards and Dwight Whitaker.
Three capsules from Sphagnum henryeuse. Two are round (unexploded) and one that has already exploded. Photo by Joan Edwards.
Habit shot of the low-growing Sphagnum moss showing reproductive heads with capsules raised above the mat by pseudopodia. Some capsules are round and not yet exploded, and some have recently exploded (cylindrical). Photo by Joan Edwards.
Scientists from Pomona College and Williams College, using high-speed video, have observed for the first time a plant that generates vortex rings. Their paper, "Sphagnum moss disperses spores with vortex rings," appears in the July 23, 2010 edition of the journal Science, published by the AAAS.
According to co-authors, Dwight Whitaker, professor of physics at Pomona College, and Joan Edwards, professor of biology at Williams College, this explosive method of spore dispersal, in which the plant creates tiny mushroom clouds, gives Sphagnum moss the added power and trajectory necessary to lift the spores to turbulent air and increase dispersal. It may also explain why this very primitive plant is so successful.
Sphagnum moss has more than 275 species and forms deep mats covering 1% of the earth's land surface. The paper also notes that it "is important in the global carbon cycle, potentially storing more carbon than any other plant genus."
For Whitaker, "What was neat about seeing the vortex ring was that at any reasonable recording speed, the movement was just a blur. The human eye can't see anything faster than 1/20 of a second. It was only when we increased the frame rate to extremes that we were able to resolve a really thin disk of spores."
"What we learned is that the Sphagnum spores explode out at 30 mph, and they stay going 30 mph as they’re launched to 80 times the height of the capsule. If you look at some of the still images from our videos, you see that the spores are compressed into a thin disk only 1/3 millimeter thick despite emerging from a capsule where they were spread out over a height of 2 mm."
The mushroom cloud rising from spore-filled capsules is a signature that the capsules are ejecting air in a vortex ring. Vortex rings are used by animals such as squid for propulsion and, in a healthy human heart to pump blood efficiently.
Prior to the study capturing the spore dispersal with high-speed video, scientists were puzzled by how Sphagnum spores reached heights that could not be explained by ballistic trajectories. The discovery that Sphagnum launches its spores into the air with a vortex ring explains how they can reach those heights where wind current can carry them indefinitely. A vortex ring is a self-sustaining flow field that can efficiently move a ‘bubble’ of one fluid through another.
Pomona College Professor of Physics
Office: (909) 607-9795
Email: Dwight Whitaker