13 February 2014

Plants Adapted/Evolved to Cope with Cold

As gardeners observe their heat and cold zones shift, they wonder how plants and animals can possibly adapt to all the changes that have happened to climate over time. Locally, the USDA hardiness zone (http://planthardiness.ars.usda.gov) moved from 6 to 7 and gardeners around the country report similar trends.

In school, we learned about the era of dinosaurs, the ice age, and, now the gradual replacement of tropical forest to dry Savannah is occurring. Birds lay eggs earlier in the year and plants are starting their spring cycles days sooner than in the past.

Henry David Thoreau recorded detailed lists of the precise blooming and leafing of several hundred flowers trees, and shrubs from 1852 to 1861. Those plants are responding to spring two-weeks earlier now (http://nyti.ms/1cV6zvv) as a result of climate change in general and due to the urban heat island created by the greater Boston population.

Tree of Life Image: www.techrivet.com
At the other end of the spectrum, researchers are studying how plants evolved to withstand winter weather. The evolutionary tree of 32,000 flowering plants they created illustrates adaptation to freezing temperatures based on leaf and stem data. 

What they found is that plants invented mechanisms and characteristics to help them thrive as they spread over the globe. We take these changes for granted. They include dying back to the roots during cold months and returning in spring – we call those plants herbaceous perennials. And the plants knew to make the adaptation even before the freezing weather arrived in their growing zone.

The researchers said that unlike animals, plants cannot relocate when the temperatures change, nor can they generate their own heat. Ice is their other challenge.

"Think about the air bubbles you see suspended in the ice cubes," said co-author Amy Zanne of the George Washington University. "If enough of these air bubbles come together as water thaws they can block the flow of water from the roots to the leaves and kill the plant."

In Moscow Idaho, a team of plant researchers including University of Idaho biologist David Tank, assembled the largest dated evolutionary tree that shows the order in which flowering plants evolved seasonal leaf-shedding.

The question scientists have been trying to answer is how woody plants like maple trees moved from their original, wet, tropical environments into cold climates.

Jeremy Beaulieu at the National Institute for Mathematical & Biological Synthesis (NIMBioS) at the University of TN is examining fossil evidence and has found that the flowering plants that first lived in warm, tropical parts of the world learned to cope as they moved to temperatures as cold as 15 below C. Beaulieu posted a 40-minute presentation at http://bit.ly/1fRhaaM explaining his work in language gardeners can easily understand.

Researchers identified the three coping mechanisms plants developed: 1) They dropped their leaves to shut down the water pathways between roots and leaves (hickory and oak); 2) Devised thinner water pathways to reduce the risk of killing air bubbles (birch and poplar), and 3) avoided the cold weather by dying to the ground, preserving their future survival/life in seeds, roots, bulbs and corms.

The scientists built two sets of data: 1) a database of 49,064 species listing whether each species maintains a stem above ground loses its leaves and changes the width of the water-carrying pathway; and 2) whether the plant was ever exposed to freezing. (Look up your climate at www.ncdc.noaa.gov.)

The researchers developed an evolutionary tree of 32,223 plant species. It is the most comprehensive view of flowering plant evolutionary history to date and is available as an interactive graphic at http://www.onezoom.org.

Their future research will focus on how plants adapt to drought and heat.
Resources -
Plants adapt to freezing weather http://bit.ly/1fHKnoVl
National Evolutionary Synthesis Center http://www.nescent.org/
Tree of Life - Khan Academy video http://bit.ly/1g2iWV8
Climate change http://1.usa.gov/1c41fBT and http://1.usa.gov/1nazxIO

Interactive site Climate Change http://ccafs.cgiar.org/bigfacts2014/#

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