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Plants regrown after 400 years in 'freezer'

Deep thaw After four centuries in nature's freezer, ancient plants uncovered by the rapid retreat of Canadian glaciers have been regenerated by scientists.

Dr Catherine La Farge and colleagues from the University of Alberta discovered intact bryophyte (moss) communities uncovered by the retreat of Tear Drop Glacier on Ellesmere Island in the Canadian Arctic Archipelago.

Their research is published today in Proceedings of the National Academy of Sciences .

Glaciers on the island have been retreating three to four metres each year, suddenly exposing vegetation that has been entombed since the Little Ice Age (LIA), which took place between 1550 and 1850AD.

The successful regrowth of these exposed plants offers new insight into polar ecosystems and how they are recolonised after rapid glacier loss.

La Farge says while many of the plants were blackened from being under the ice, they were structurally intact, and some even had a striking greenish tinge.

"Some of the populations that were emerging from the glacier actually appeared to have some 'greeness'," La Farge says.

"When we got the material back in the lab we observed green lateral branch growth from old LIA stems, which suggested they might actually still be viable. So we decided to try culturing the material," says La Farge.

Built for survival

After radiocarbon dating to confirm the exhumed plants' age, seven specimens, representing four distinct taxa, were ground up and sprinkled on to petri dishes full of potting mix, where they started to grow.

"Bryophytes are built for survival in extreme environments in ways that vascular plants are not," says La Farge, adding that mosses, one of three bryophyte lineages, are particularly well adapted to extreme environments because of their tolerance for both freezing and desiccation.

"It has to do with their cell physiology, which provides special cell-repair mechanisms after desiccation."

She says brophytes are able to revive themselves after periods of drought or being frozen because they have totipotent cells -- meaning that any viable cell can regress to an initial germination state.

"This gives the cell the capacity to regenerate an entire new plant", La Farge says, through the earliest growth stages of the thread-like chain of cells known as the protonema to a leafy gametophyte.

Critical function

The results suggest that bryophytes, among the earliest land plants, may be far more resilient than previously thought, and likely contribute to the establishment, colonisation, and maintenance of polar ecosystems.

"These underestimated, simple plants are critical for maintaining polar ecosystems and form rich biological reservoirs beneath glaciers," says La Farge, adding that previous reports of subglacial vegetation exhumed from glacial margins have considered the material dead.

"It has been always been viewed simply as an organic substrate, but never as containing viable tissue that could regrow."

She says that mosses are programmed to live in extreme environments.

"Severe winds rip across the landscape and tear apart populations; winter's deep freeze shuts them down for eight months of the year; and harsh exposure can desiccate the plants.

"[By comparison] survival under subglacial conditions might even seem pleasant."

It is yet to be determined how long bryophytes could be cryopreserved and still regenerate.

"This depends on the taphonomy -- how the population was entombed, buried, and preserved -- and can't be ruled out in [any] glaciated or permafrost environments," she believes.

"The potential [for regeneration] is there if the cells have remained frozen for a continuous span of time -- 5000, 10,000, 30,000 years, or even more."