Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Confirmed: How plant communities endure stress

31.01.2013
The Stress Gradient Hypothesis holds that as stress increases in an ecosystem, mutually supportive interactions become more significant and negative interactions, such as competition, become less so.

The idea has been hotly debated but is now backed by a review of hundreds of studies co-authored in Ecology Letters by Mark Bertness, professor of biology at Brown, who first formally proposed the hypothesis in 1994. The time has come, he said, to test its application and predictive value.

Ecology is rife with predation, competition, and other dramatic “negative interactions,” but those alone do not determine the course life on Earth. Organisms sometimes benefit each other, too, and according to the Stress Gradient Hypothesis, their “positive interactions” become measurably more influential when ecosystems become threatened by conditions such as drought. Ecologists have argued about the hypothesis ever since Brown University ecologist Mark Bertness co-proposed it in 1994; Bertness says a large new global meta-analysis he co-authored in Ecology Letters definitively shows that it is true.

The evidence, principally analyzed by former Brown visiting graduate student Qiang He of Shanghai Jiao Tong University in China, comes from 206 studies of 727 shifts of plant interactions amid varying degrees, or gradients, of stress on six continents. Examining the data from each paper and contacting original authors when necessary, He determined the overall trends across the many experiments.

In the vast majority of studies, as stress increased, the significance of interactions shifted toward mutual support in that positive interactions, such as those that promoted neighbors’ survival, strengthened in influence, and negative interactions, such as those that hindered neighbors’ growth, weakened. In some studies, stress did not change interactions, but negative interactions never increased as stress did, no matter what kinds of plants were involved, what kinds of conditions they were under, or where they were.

Stress in Sardinian sand dunes

Grasses, trees and shrubs have obvious differences, but in times of stress their communities exhibit less negative competitive pressure and more facilitative, positive interaction.“Our results show that plant interactions generally change with increased environmental stress and always in the direction of an outright shift to facilitation (typical for survival responses) or a reduction in competition (typical from growth responses),” the authors wrote in the paper published online. “We never observed an increase in competition at higher stress. These findings were consistent across fitness measures, stress types, growth forms, life histories, origins, climatic zones, ecosystems and methodologies.”

Analyses of studies of grasses, trees, and shrubs, for example, found that despite the obvious differences among these plant types, they all shifted toward less negative or more positive interactions.

“Typically, highly competitive species [e.g., grasses] have decreased competitive or neutral effects at high stress, whereas less competitive species [e.g., trees] have strong facilitative effects at high stress,” the authors wrote.

Overall, the researchers found, studies with observations of greater degrees of stress increase — “longer” stress gradients — also observed greater degrees of shift toward positive interactions.

The hypothesis and the importance of positive interactions in ecology began to occur to Bertness in the 1970s and 1980s. As a junior faculty member at Brown, along the shores of Rhode Island, he noticed that seaweeds and barnacles would never survive the heat stress above the tides in isolation. They could only persist in groups, suggesting that with stress, organisms were better off together — despite their competition — than apart.

It’s the same reason why sparsely planted gardens wilt in hot, dry conditions while more densely planted gardens survive. Mutually beneficial soil shading becomes more important than competition for that soil moisture when it becomes scarce.

Bertness published the Stress Gradient Hypothesis in Trends in Ecological Evolution with Ray Callaway, then a graduate student at the University of California–Santa Barbara. Callaway is now a professor at the University of Montana.

A shift in research?

Mussel beds in Patagonia

Hundreds of studies over two decades from sites around the world suggest that the Stress Gradient Hypothesis can be employed as a rule of thumb. “We’re no longer in the casual, earlier stages of ecology,” says biologist Mark Bertness.Nearly two decades later with so much evidence now assembled, Bertness said, ecologists should feel confident enough in the Stress Gradient Hypothesis to employ it as a “rule of thumb.” Rather than continuing to debate whether the hypothesis is valid, he said, researchers could now focus on crafting experiments to probe how much predictive value the hypothesis has and test its applications to conservation biology.

The hypothesis suggests, for example, that marine ecosystem managers who want to help tropical fish should focus on sustaining foundational species in the ecosystem, such as corals. With the ecosystem’s foundation shored up the natural tendency among species toward greater positive interactions under stress should allow the fish to weather stress better.

“We’re no longer in the casual, earlier stages of ecology,” Bertness said. “In our lifetimes we’re watching Caribbean coral reefs die, kelp forests die, and salt marshes and sea grass beds being decimated. We need to figure this stuff out quickly. These are no longer intellectual arguments without consequence.”

In other words, with nature under stress, Bertness hopes that He’s efforts to pull together the available data will lead ecologists to pull together so that they can apply the guidance the hypothesis provides.

In addition to He and Bertness, the paper’s other author is Brown postdoctoral scholar Andrew Altieri.

He’s visiting scholarship at Brown was funded by the Shanghai Jiao Tong University Visiting Scholar Fellowship.

Editors: Brown University has a fiber link television studio available for domestic and international live and taped interviews, and maintains an ISDN line for radio interviews. For more information, call (401) 863-2476.

David Orenstein | EurekAlert!
Further information:
http://www.brown.edu

More articles from Ecology, The Environment and Conservation:

nachricht Dispersal of Fish Eggs by Water Birds – Just a Myth?
19.02.2018 | Universität Basel

nachricht Removing fossil fuel subsidies will not reduce CO2 emissions as much as hoped
08.02.2018 | International Institute for Applied Systems Analysis (IIASA)

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Molecules Brilliantly Illuminated

Physicists at the Laboratory for Attosecond Physics, which is jointly run by Ludwig-Maximilians-Universität and the Max Planck Institute of Quantum Optics, have developed a high-power laser system that generates ultrashort pulses of light covering a large share of the mid-infrared spectrum. The researchers envisage a wide range of applications for the technology – in the early diagnosis of cancer, for instance.

Molecules are the building blocks of life. Like all other organisms, we are made of them. They control our biorhythm, and they can also reflect our state of...

Im Focus: Spider silk key to new bone-fixing composite

University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.

Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.

Im Focus: Writing and deleting magnets with lasers

Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.

Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...

Im Focus: Gamma-ray flashes from plasma filaments

Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.

The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...

Im Focus: Basel researchers succeed in cultivating cartilage from stem cells

Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.

Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

Unique scope of UV LED technologies and applications presented in Berlin: ICULTA-2018

12.04.2018 | Event News

IWOLIA: A conference bringing together German Industrie 4.0 and French Industrie du Futur

09.04.2018 | Event News

 
Latest News

Structured light and nanomaterials open new ways to tailor light at the nanoscale

23.04.2018 | Physics and Astronomy

On the shape of the 'petal' for the dissipation curve

23.04.2018 | Physics and Astronomy

Clean and Efficient – Fraunhofer ISE Presents Hydrogen Technologies at the HANNOVER MESSE 2018

23.04.2018 | Trade Fair News

VideoLinks
Science & Research
Overview of more VideoLinks >>>