Most desert plants, including cacti, rely on extensive root systems to mop up scarce groundwater. But the desert moss Syntrichia caninervis collects fresh water straight from the atmosphere. Tiny fibres attached to the tips of the moss leaves, known as awns, allow S. caninervis to harvest fog and mist droplets, says Tadd Truscott of Utah State University, who filmed the plant's drinking behaviour.
Truscott and his colleagues used an environmental scanning electron microscope and camera to study how these delicate awns, which are between 0.5 and 2 millimetres long, capture atmospheric water. They studied S. caninervis growing in the Great Basin in the US and in the Gurbantünggüt desert in China, but it is also widely found in other northern hemisphere deserts.
The camera images show water vapour condensing on nano-sized grooves on the surface of the awns. Miniature barbs then push this water into larger droplets that move along the length of the awn into the leaf. "The droplet can travel from the awn to the leaf as fast as 10 to 20 millimetres per second," says Truscott.
Two other plant species have previously been found to possess fog-harvesting abilities - the cactus Opuntia microdasys and the alpine plant Cotula fallax - but S. caninervis is the first species in which a detailed mechanism involving barbs and grooves has been elucidated.
Scientists can try to replicate these plants' mechanisms in order to build novel water collection systems, says Truscott. "Our lab has already started making artificial awns to determine if these structures can be man-made," he says.
The greatest beneficiaries of fog-harvesting devices would be people in developing countries with limited access to clean drinking water, says Jas Pal Badyal of Durham University, who is trying to mimic the mechanisms of C. fallax.
Even dry places like the Namib desert in Africa have regular fog episodes, meaning that clean water vapour could be harvested and stored, he says. "The idea is to trap pure water from air."
Journal reference: Nature Plants, DOI: 10.1038/nplants.2016.76