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Flower power makes tropics cooler, wetter


June 24, 2010
By Amanda Ryder

leafNEWS HIGHLIGHT

Flower power makes tropics cooler, wetter

The world is a cooler, wetter place because of flowering plants,
according to new climate simulation results published in the journal Proceedings of the Royal Society B.

June 24, 2010 – The world is a cooler, wetter place because of flowering plants,
according to new climate simulation results published in the journal Proceedings of the Royal Society B.
The effect is especially pronounced in the Amazon basin, where
replacing flowering plants with non-flowering varieties would result in
an 80 per cent decrease in the area covered by ever-wet rainforest.

The
simulations demonstrate the importance of flowering-plant physiology to
climate regulation in ever-wet rainforest, regions where the dry season
is short or non-existent, and where biodiversity is greatest.

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“The vein density of leaves within the flowering plants is much, much
higher than all other plants,” said the study’s lead author, C. Kevin
Boyce, Associate Professor in Geophysical Sciences at the University of
Chicago. “That actually matters physiologically for both taking in
carbon dioxide from the atmosphere for photosynthesis and also the loss
of water, which is transpiration. The two necessarily go together. You
can’t take in CO2 without losing water.”

This higher vein density
in the leaves means that flowering plants are highly efficient at
transpiring water from the soil back into the sky, where it can return
to Earth as rain.

“That whole recycling process is dependent
upon transpiration, and transpiration would have been much, much lower
in the absence of flowering plants,” Boyce said. “We can know that
because no leaves throughout the fossil record approach the vein
densities seen in flowering plant leaves.”

For most of biological
history there were no flowering plants—known scientifically as
angiosperms. They evolved about 120 million years ago, during the
Cretaceous Period, and took another 20 million years to become
prevalent. Flowering species were latecomers to the world of vascular
plants, a group that includes ferns, club mosses and confers. But
angiosperms now enjoy a position of world domination among plants.

“They’re basically everywhere and everything, unless you’re talking about high altitudes and very high latitudes,” Boyce said.

Dinosaurs
walked the Earth when flowering plants evolved, and various studies
have attempted to link the dinosaurs’ extinction or at least their
evolutionary paths to flowering plant evolution. “Those efforts are
always very fuzzy, and none have gained much traction,” Boyce said.

Boyce
and Lee are, nevertheless, working toward simulating the climatic
impact of flowering plant evolution in the prehistoric world. But
simulating the Cretaceous Earth would be a complex undertaking because
the planet was warmer, the continents sat in different alignments and
carbon- dioxide concentrations were different.

“The world now is really very different from the world 120 million years ago,” Boyce said.

 

Building the Supercomputer Simulation

 

So
as a first step, Boyce and co-author with Jung-Eun Lee, Postdoctoral
Scholar in Geophysical Sciences at UChicago, examined the role of
flowering plants in the modern world. Lee, an atmospheric scientist,
adapted the National Center for Atmospheric Research Community Climate
Model for the study.

Driven by more than one million lines of
code, the simulations computed air motion over the entire globe at a
resolution of 300 square kilometers (approximately 116 square miles).
Lee ran the simulations on a supercomputer at the National Energy
Research Scientific Computing Center in Berkeley, Calif.

“The
motion of air is dependent on temperature distribution, and the
temperature distribution is dependent on how heat is distributed,” Lee
said. “Evapo-transpiration is very important to solve this equation.
That’s why we have plants in the model.”

The simulations showed
the importance of flowering plants to water recycling. Rain falls,
plants drink it up and pass most of it out of their leaves and back
into the sky.

In the simulations, replacing flowering plants
with non-flowering plants in eastern North America reduced rainfall by
up to 40 per cent. The same replacement in the Amazon basin delayed
onset of the monsoon from Oct. 26 to Jan. 10.

“Rainforest
deforestation has long been shown to have a somewhat similar effect,”
Boyce said. Transpiration drops along with loss of rainforest, “and you
actually lose rainfall because of it.”

Studies in recent decades
have suggested a link between the diversity of organisms of all types,
flowering plants included, to the abundance or rainfall and the
vastness of tropical forests. Flowering plants, it seems, foster and
perpetuate their own diversity, and simultaneously bolster the
diversity of animals and other plants generally. Indeed, multiple
lineages of plants and animals flourished shortly after flowering
plants began dominating tropical ecosystems.

The
climate-altering physiology of flowering plants might partly explain
this phenomenon, Boyce said. “There would have been rainforests before
flowering plants existed, but they would have been much smaller,” he
said.

Citation: C. Kevin Boyce and Jung-Eun Lee, “An
exceptional role for flowering plant physiology in the expansion of
tropical rainforests and biodiversity,” published online June 16, 2010,
in the Proceedings of the Royal Society B.


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