"The take-home message is that junipers are the most drought-resistant group that has ever been studied," said Robert Jackson, a professor of global environmental change and biology at Duke's Nicholas School of the Environment and Earth Sciences.
"We examined 14 species from the U.S. and Caribbean, and they're all relatively drought-resistant -- even ones in the mountains of Jamaica that get hundreds of inches of rain a year," he said.
"They've been expanding for about 100 years in some places, and drought plays a role in that," added Jackson, who is corresponding author of the new report published Feb. 27 in the American Journal of Botany's online edition. "For example, recent droughts have decimated pinyon pine populations in pinyon-juniper woodlands of the Southwestern U.S. but left the junipers relatively unscathed."
Many juniper species -- including several popularly known as cedars -- "are invading drier habitats and increasing in abundance where they already exist by surviving droughts that other conifers cannot," the report said.
The work was funded by the National Science Foundation, Duke University and the Andrew W. Mellon Foundation.
To understand why junipers are so successful, Jackson's graduate student Cynthia Willson and Duke associate biology professor Paul Manos assessed structural and genetic features in the 14 species that can explain their special drought tolerance.
They found a key structural adaptation in junipers: resistance to what scientists call "cavitation" -- a tendency for bubbles to form in the water-conducting xylem tissues of plants.
Water is sucked through xylem tissues under a partial vacuum, "so it's almost like a rubber band being stretched out," explained Jackson. "The dryer the conditions, the greater the tension on that 'rubber band' and the more likely that it will snap. If it snaps, air bubbles can get into the xylem."
The scientists found that xylem tissues of juniper species tend to be reinforced with extra woody material to prevent rupture. Such rupturing can introduce bubble-forming air either through seepage from adjacent cavities or by coming out of solution from the water itself, Jackson said.
The scientists also determined that the more cavitation-resistant Juniper species have thicker but narrower leaves -- a trait known as low specific leaf area (SLA) -- and live primarily in the western United States.
"Plants in drier environments typically have lower SLA," said Willson, the study's first author, who having completed her Ph.D. at Duke is now a student at North Carolina State University's College of Veterinary Medicine. "We found that junipers from the driest environments were more drought resistant and also had the lowest SLA."
Their research found that the most cavitation-resistant species is the California juniper, which grows in California's Mojave Desert, while the least resistant is the eastern red cedar -- the most widespread conifer in the relatively-moist eastern U.S.
While less drought-tolerant than other junipers, eastern red cedars still handle dry spells well and are in fact invading into Midwestern states including Nebraska, Jackson noted. Juniper species growing in wet parts of the Caribbean also benefit from drought tolerance because they "tend to grow in shallow, rocky soils that don't hold a lot of water," Jackson said.
In parts of the Southwest undergoing an extended drying period, junipers are edging out another hardy, water-thrifty conifer -- the pinyon pine. "They're both very drought- resistant, but the pinyons aren't as resistant as the junipers are," Jackson said.
The scientists also investigated how and where these tree types evolved their collective drought tolerance by analyzing each juniper species' DNA. That analysis found that junipers evolved into different species relatively recently, separating into eastern and western groups -- technically called "clades."
"The center of diversity for junipers is in arid regions of Mexico," said Willson. "The fact that many juniper species seem to be more drought-resistant than necessary for their current range suggests that a common ancestor of those two clades was also quite drought-resistant."
Monte Basgall | EurekAlert!
Transport of molecular motors into cilia
28.03.2017 | Aarhus University
Asian dust providing key nutrients for California's giant sequoias
28.03.2017 | University of California - Riverside
The Institute of Semiconductor Technology and the Institute of Physical and Theoretical Chemistry, both members of the Laboratory for Emerging Nanometrology (LENA), at Technische Universität Braunschweig are partners in a new European research project entitled ChipScope, which aims to develop a completely new and extremely small optical microscope capable of observing the interior of living cells in real time. A consortium of 7 partners from 5 countries will tackle this issue with very ambitious objectives during a four-year research program.
To demonstrate the usefulness of this new scientific tool, at the end of the project the developed chip-sized microscope will be used to observe in real-time...
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
28.03.2017 | Life Sciences
28.03.2017 | Information Technology
28.03.2017 | Physics and Astronomy