Due to freeze-thaw cycles in winter, water flow is disrupted when air bubbles form in the conductive xylem of the trees. Because of that, some of these tall conifers are seriously stressed for water when they are practically standing in a lake of it, scientists from Oregon State University and the U.S. Forest Service concluded in a recent study.
It’s not “drought stress” in a traditional sense, the researchers said, but the end result is similar. Trees such as Douglas-fir actually do better dealing with water issues during summer when they simply close down their stomata, conserve water and reduce their photosynthesis and growth rate.
“Everyone thinks that summer is the most stressful season for these trees, but in terms of water, winter can be even more stressful,” said Katherine McCulloh, a research assistant professor in the OSU Department of Forest Ecosystems and Society.
“We’ve seen trees in standing water, at a site that gets more than two meters of rain a year, yet the xylem in the small branches at the tops of these trees can’t transport as much water as during the summer,” McCulloh said.
The ease with which water moves through wood is measured as the “hydraulic conductivity,” and researchers generally had believed this conductivity would be the lowest during a conventional drought in the middle of summer. They found that wasn’t the case.
“We thought if there was a serious decline in conductivity it would have been from drought,” said Rick Meinzer, a researcher with the Pacific Northwest Research Station of the USDA Forest Service, as well as OSU. “It was known that air bubbles could form as increased tension is needed in the xylem to pull water higher and higher. But it turns out that freezing and thawing caused the most problems for water transport.”
Studies such as this are important, the scientists said, to better understand how forests might respond to a warmer or drier climate of the future. And although this might imply that these conifers could be more resistant to drought than had been anticipated, the researchers said it’s not that simple.
“If the climate warms, we might actually get more of these winter cycles of freezing and thawing,” McCulloh said. “There’s a lot of variability in the effects of climate we still don’t understand.
“One of the most amazing things these trees can do is recover from these declines in conductivity by replacing the air bubbles with water,” she said. “We don’t understand how they do that at the significant tensions that exist at those heights. We’re talking about negative pressures or tensions roughly three times the magnitude of what you put in your car tires.”
When the field research on this study was done in 2009, the area actually experienced a historic heat wave during August when temperatures in the Willamette Valley hit 108 degrees. During such extreme heat, trees experienced some loss of hydraulic conductivity but largely recovered even before rains came in September. By contrast, greater loss of hydraulic conductivity was observed in the middle of winter.
The study was done at the Wind River Canopy Crane Research Facility, and published in the American Journal of Botany. The research was supported by the National Science Foundation.
“The commonly held view is that the summer months of the Pacific Northwest are extremely stressful to plants,” the researchers wrote in their conclusion.
“Yet, our results indicated that the winter months are more stressful in terms of hydraulic function, and suggest that perhaps an inability to recover from increase in native embolism rates over the winter may cause greater branch dieback in old-growth trees than shifts in summer climate.”
About the OSU College of Forestry: For a century, the College of Forestry has been a world class center of teaching, learning and research. It offers graduate and undergraduate degree programs in sustaining ecosystems, managing forests and manufacturing wood products; conducts basic and applied research on the nature and use of forests; and operates 14,000 acres of college forests.
Kate McCulloh | EurekAlert!
Energy crop production on conservation lands may not boost greenhouse gases
13.03.2017 | Penn State
How nature creates forest diversity
07.03.2017 | International Institute for Applied Systems Analysis (IIASA)
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