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Experts expose secret life of mating mosses

Inviting scent Female moss plants exude a scent that attracts fertilising arthropods, new research has found.

Plant evolutionary ecologist Dr Sarah Eppley, of Portland State University, and colleagues, report their findings today in the online ahead of print edition of Nature.

"This positive interaction between mosses and arthropods could have played a key role in the diversification of land plants," says Eppley.

Mosses were among the first plants to inhabit the Earth 450 million years ago. Unlike flowering plants, which emerged 200 million years later, mosses do not have a vascular system and don't grow very tall.

Eppley and colleagues studied a common moss called Ceratodon purpureus, which grows to 1 centimetre high and has leaves just one cell thick that allow water to diffuse straight into them.

The moss grows in damp areas all over the world, including in forests, gardens and on roofs. Instead of pollen, it has sperm in little packets on the male plants that needs to somehow get to female plants.

Theories of fertilisation

Until relatively recently scientists thought that moss fertilisation required water. It was thought rain would break open the packets of sperm, allowing sperm to float upwards and swim over to the female.

But some research has suggested ancient arthropods, called springtails, help transfer sperm to the female - in a similar way that pollinators help fertilise flowering plants.

Springtails evolved at the same time as mosses, and just like the mosses they are found all over the world in great numbers - a hundred thousand per square metre in the forest Eppley and colleagues studied.

The researchers wanted to confirm whether or not springtails were involved in fertilising mosses, and if so, what cues the mosses used to attract their fertilising arthropod friends.

They also wanted to determine whether fertilising springtails were important regardless of the presence of water.

"If there is rain occurring, maybe the arthropods aren't really important," says Eppley.

Experiments

Eppley and colleagues grew moss in terrariums, some of which had no rainwater or springtails, some of which had one or the other, and some that had both.

Then they looked at how many moss fruit (sporophytes) were produced under each condition.

The researchers found in the absence of water or springtails very little fruit was produced. The presence of springtails or water gave "pretty high" levels of fruit.

But was most interesting is that when water and springtails were both present, the number of fruit produced more than doubled.

Eppley says this is probably because the water helps the sperm to be released into the environment where it can come in contact with the springtails.

Scented moss

Eppley and colleagues also used GCMS (gas chromatography mass spectroscopy) to identify scents produced by both male and female moss plants, and tested which scents attracted the springtails.

Male and female plants were placed in two different chambers of an olfactometer under a filter, which allowed volatile scents to rise up through it.

Springtails were allowed to run around freely on top of the filter paper and head towards the scent they were attracted to.

"We did this over and over again and 65 per cent of the time they would choose the side with the female plant in it," says Eppley.

Further studies will explore what exactly is producing the scent - it could be microbes within the plant rather than the plant itself, says Eppley.

She would also like to test if the arthropod-attracting scent is present across all species of moss.

If so, says Eppley, this suggests scent-based pollination-like processes could have evolved early and were key to allowing plants to colonise land, even when it was dry.