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    Study: Plants Might Lack Traits Needed to Cope With Climate Change

    Plants have evolved defenses, like dropping their leaves, to adapt to cold, harsh climates. (Simon Uribe-Convers)
    Plants have evolved defenses, like dropping their leaves, to adapt to cold, harsh climates. (Simon Uribe-Convers)
    Rosanne Skirble
    A new study suggests that modern flowering plants, trees and agricultural crops may not have the characteristics, or the time, to respond to rapid human-induced climate change.
     
    The report in Nature looks at how plants evolved to cope with cold in the past, but finds these same mechanisms may not provide the same defense against human-induced climate change.

    Survival traits
     
    Flowering plants lived in warm tropical climates 243 million years ago. Since then, they have spread across the planet into much harsher places. George Washington University ecologist Amy Zanne and her colleagues wanted to understand how the plants survived in a colder environment. 

    • Sunrise through an oak-hickory forest canopy at Tyson Research Center, Washington University in St. Louis, Missouri. (Jonathan Myers)
    • The leaves of a sugar maple start to yellow as winter approaches, Tyson Research Center, Washington University in St. Louis, Missouri. (Jonathan Myers)
    • An ornamental cherry tree loses its leaves in the fall at the Tidal Basin, Washington, DC. (Amy Zanne)
    • A frost covered dandelion head spreads as winter arrives at the University of Idaho Arboretum, Moscow, Idaho. (Simon Uribe-Convers)
    • A birch leaf turns a bright yellow as winter approaches, Gateway Arch, St. Louis, Missouri. (Amy Zanne)
    • Maple leaves change colors before they fall in Rock Creek Park, Washington, DC. (Amy Zanne)
    • Early winter brings out the reds and oranges on sugar maple trees at the Gateway Arch, St. Louis, Missouri, USA. (Amy Zanne)
    • Buckeye leaves emerge in the spring after the winter frost at Forest Park, St. Louis, Missouri. (Amy Zanne)
    • Newly emerged tulip poplar leaves in spring after winter frost at Joyce Kilmer Memorial Forest, Robbinsville, North Carolina. (Amy Zanne)

    They identified three traits that help them do that: dropping their leaves before the winter chill, narrowing the cells that transport water from the roots to the leaves, and dying back to the ground and re-sprouting from their roots or seeds in the spring.     
     
    “The next bit was, we wanted to not just look at where species are today and whether they are seeing freezing or not, but to try to understand the evolution of these characteristics and the order of the evolution of those characteristics or those traits,” Zanne said.  

    Evolutionary tree

    To do that, the researchers constructed the largest-ever time-scaled evolutionary tree of 32,000 plant species. They then compared the emergence of those adaptive traits with big changes in the Earth's climate to reconstruct how plants evolved with the cold as they spread across the globe. 

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    “We saw for all three of the traits, there was a really strong support for finding a shift into freezing and also a shift in the trait. And so to tough it out and deal with the cold, what they did was they made these narrower pipes so that they wouldn’t get these air bubbles that blocked the water through the stems," Zanne said. "So they could maintain that stem by keeping those small pipes.  Or what they did was they dropped their leaves. So they didn’t have to keep their leaves from year to year. Or the third thing that they did was they avoided or hid from the cold altogether by becoming herbaceous.” 

    Herbaceous plants have leaves and stems that die back to the ground in winter. 
     
    Zanne says one of the most significant findings was that the changes occurred even before the plants' range extended into colder environments.  
     
    “So what we found was that plants before they even confronted the cold, they typically already had skinnier pipes and they already had become herbaceous," she said. "So they responded already to some other pressure. And so maybe it was a dry environment or something like that and that these characteristics, these traits were then really useful for dealing with the cold. So they went into the cold well armed to handle those cold temperatures.”  
     
    Zanne and her team also plan to study plants in warm or dry environments. The study suggests that modern flowering plants, trees and agricultural crops may not have the traitsor the time neededto cope with human-induced climate change.

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