Rip Van Winkle, the titular ne'er-do-well of Washington Irving's 1819 short story, famously spent 20 years napping in a forest. This lengthy slumber, apparently triggered by ghost liquor, caused Van Winkle to sleep through the American Revolutionary War.
Nearly two centuries later, scientists are shedding light on plants that do something similar in real life. A surprisingly diverse mix of plants around the world can live dormant underground for up to 20 years, researchers report in the journal Ecology Letters, a strategy that allows the plants to survive hard times by simply napping until things get better.
At least 114 species from 24 plant families are capable of this trick, in which a plant abandons photosynthesis to focus on survival in the soil. It's a way for plants to hedge their bets, the study's authors explain, by accepting certain short-term hardships — like missed opportunities to grow and reproduce — for the longer-term benefits of avoiding mortal dangers on the surface.
"It would seem to be paradoxical that plants would evolve this behavior, because being underground means they cannot photosynthesize, flower or reproduce," says co-author Michael Hutchings, an ecology professor at the University of Sussex, in a statement. "And yet this study has shown that many plants in a large number of species frequently exhibit prolonged dormancy."
So how do these Rip Van Winkle plants survive for up to 20 years without sunlight? Many species have found other ways to endure dormancy, Hutchings says, especially "by evolving mechanisms enabling them to obtain carbohydrates and nutrients from soil-based fungal associates." Befriending soil fungi, he adds, "allows them to survive and even thrive during dormant periods."
This strategy is used by many orchid species (including the lady's slipper orchids pictured above), along with a wide variety of other plant types. It typically occurs in only part of a population or species during any given year, the researchers note, so the broader population can keep growing and reproducing while the designated survivors wait underground as backup.
Sleep on it
Scientists have long studied dormancy in plant seeds, but the subterranean sabbaticals of adult plants are much less widely known and understood. The new study is the first detailed analysis, its authors say, to investigate the causes, ecological functions and evolutionary significance of dormancy in adult plants. The reasons for going dormant vary among populations and species, including threats like herds of hungry herbivores and poor conditions during the growing season.
The researchers had expected dormancy to be more common at higher latitudes and altitudes, where cold weather tends to shorten the growing season, but their findings suggest the opposite. Plants seem to use the strategy more often near the equator, they report, where dangers like disease, competition, herbivores and fire are often more severe. "In fire-prone areas, there appears to be an advantage to plants remaining dormant and then sprouting after fire, when favorable conditions exist for growth and flowering," says co-author Eric Menges, a research biologist at the Archbold Biological Station in Florida.
The study also reveals, thanks to phylogenetics, that dormancy has evolved multiple times in the history of land plants. "This suggests not only that it has proved beneficial under many different ecological circumstances," Hutchings says, "but also that its evolution may be achievable through the occurrence of a small number of mutations at only a few genetic loci."
The calculus behind these interludes is still hazy, Hutchings adds, noting that more research will be needed before we can really understand a plant's "decision to go dormant." And that research could prove valuable, because unlike the notoriously lazy Rip Van Winkle, many of these plants have important work to do.
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