HIV virus in disguise tricks immune system, Marie Larsson is Professor of Molecular Virology

Name: Marie LarssonTitle: Professor of Molecular Virology
Department: IKE

CONTACT

Phone: +46 (0)10-103 10 55
E-mail: marie.larsson@liu.se

Address:
Linköping University
Department of Clinical and Experimental Medicine
Virology
SE-581 85 Linköping
Sweden

Marie Larsson is Professor of Molecular Virology. Her research is in the area of immunovirology, specifically HIV research with focus on the immunomodulatory effect this virus has on dendritic cells and T cells. She has also ongoing projects exploring new adjuvants and vaccine constellations for cancer and virus. Furthermore, she is investigating the induction and sustainment of cancer associated inflammation and the deleterious effect this has on host immune defense.

Immunomodulatory effects of HIV-1’s interactions with DCs and T cells from

blood and mucosa
So far over 30 million people have died from HIV-1 infection (figure 1), the majority of them in the developing countries, and this epidemic is still cause for major concern. The existing antiretroviral therapy dampens the infection and the destruction of the immune system, i.e. AIDS, but does not cure the disease. Sadly, this therapy is not available to all HIV infected and is a very expensive lifelong commitment with severe side effects.

A vaccine blocking HIV infection is theDendritic cell sought-after solution but there is no hope that we will have such a vaccine in the near future. Instead we can hope for a therapy that induces a potent long lasting immune response consisting of CD4+ and CD8+ T cells, two types of control cells involved in the immune defense, that have proven to be important to control the infection. There exists a unique cell in all tissues in our bodies, the dendritic cell (DC) (Figure 2) with unique ability to activate T cells so they can perform their job in the body. DCs in the vaginal and rectal tissues are one of the first cells to encounter HIV during intercourse with an infected individual (Figure 3 and 4). Unfortunately, HIV hijacks the DCs, which makes this cell responsible for spreading the virus to interacting T cells in the body which provokes HIV-infection of T cells and cell death when it should be initiating immune responses to fight the infection.DC HIV

My research aspires to elucidate the mechanisms behind the immunomodulatory effects HIV exerts on DCs and on their ability to activate T cells. Focus will be on; Elucidation of the mechanisms involved in HIV’s binding to and uptake by DCs and the subsequent degradation that leads to DC antigen presentation of HIV peptides for activation of HIV specific T cells. Elucidation of the mechanisms responsible for the negative effects HIV exerts on DCs and if presence of HIV virions during DC T cell priming impairs the T cell function. Elucidate the effect opsonized HIV-1 exerts on immune cells such as DCs, NK cells and T cells. Identification of receptors and cells involved in the initial HIV infection of cervical mucosa and colorectal mucosa,  and potential microbiocides that can block the initial infection, and elucidation of why HIV affects the T cells in the gut to a higher extent than the T cells in blood.

HIV will continue to kill people and have a great impact on mankind until we have a drug that can stop this infection. My ambition is that the planed research will answer some basic questions regarding the role of DCs in HIV pathogenesis and induction of potent immune response against this virus. This knowledge will guide how a vaccine/therapy needs to be constructed in order to have high efficacy.

                                                             Mucosal transmission

                                                                Cervix

Cancer research

Elucidation the role of IL-1α and the microenvironment in development of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is a common gastrointestinal malignancy with an exceptional poor prognosis and a mortality rate that nearly matches the rate of incidence. The cross-talk between PDAC and stroma cells, e.g. cancer associated fibroblasts (CAF), and immune cells, may create an environment with chronic inflammation augmenting tumor transformation and maintenance.

In PDAC, more than 70% of the total tumor mass can consist of fibrotic stroma, which makes CAFs the major component in this cancer. PDAC inflammatory environment consists of many mediators, e.g. IL-1, COX-2, IL-6, and CXCL8, and some of these factors correlate to tumor development and poor prognosis. Of note, elevated expression of IL-1 in tumors has been associated with more aggressive disease. Several studies, including ours have reported that dendritic cells (DCs), one of the immune cells found in the tumor microenvironment, show phenotypic and functional abnormalities when isolated from tumor bearing animals and individuals with PDAC. Recent findings provided some evidence that the COX-2 metabolite PGE2 is involved in the upregulation of immunomodulatory factors in DCs impairing their T cell stimulatory ability. The aims are to examine the receptor-ligands and signaling pathways involved in the cross talk between stroma cells, i.e. CAFs, and PDAC cells giving rise to the inflammatory environment and creating an environment sustaining the PDAC. To examine the role IL-1 cytokine family and effects these cytokines cell signaling have on creating the inflammatory environment and in tumor development and survival. To examine whether neutralization of IL1 signaling pathway enhances the survival and quality of life for individuals with pancreatic cancer.

The information gained from the proposed research will help us understand the mechanisms underlying the development of PDAC and the effect this solid tumor exert on the body and may help designing therapies for PDAC.

Source: Linköping University

Scheduling tool a big help in healthcare

The HIV virus avoids the body’s immune cells by disguising itself using proteins that normally take part in the defence against infections. These are the findings of research conducted at the Division of Molecular Virology.

Professor Marie LarssonThese “complement proteins” are soluble molecules that attach themselves to foreign particles and those of the body in different patterns. These patterns help the immune system to identify and attack dangerous intruders such as viruses and bacteria.

Phd student Rada EllegårdInstead, HIV exploits the complement proteins present in all body fluids in order to make its way into the body tissues without being attacked. It was known previously that infections are much more effective if the virus is surrounded by the bodily fluids normally present in blood or sexual contagion than if it is isolated in a laboratory environment. In an article in the Journal of Immunology Marie Larsson, professor of molecular virology (left) and PhD student Rada Ellegård (right) provide an explanation of this phenomenon.

“The ability to use our complement proteins in this way is probably key to the success of HIV in being transmitted. We are currently carrying out further work to investigate these mechanisms in the male genital mucous membrane – the tissue where the virus infection takes place in sexual transmission,” says Ms Larsson.

The first thing HIV particles come into contact with is dendritic cells, immune cells that function as sentry posts. Their job is to identify viruses as dangerous and hostile to the body, and to respond by producing the substances that combat infections and moving to a lymph node to set a specific immune defence in motion.

In the case of HIV, this process does not seem to work very well. The disguise stops the dendritic cells recognising the virus, which instead establishes an infection in the mucous membrane and uses the movement to the lymph nodes as a way to spread around the whole body.

As more and more cells are infected and killed, the virus slowly breaks down our immune system. Without treatment this sequence of events leads to AIDS, a condition where the victim becomes extremely vulnerable to infection and where normally harmless viruses and bacteria become life-threatening.

Related content

Marie Larsson - research presentation >>

                                       HIV-illustration

When a virus is captured by a dendritic cell, it is recognised by a virus sensor that normally sets in motion infection reduction factors which inhibit the production of new virus particles (picture, left). HIV has the ability to clothe itself in complements, a type of protein present in our bodily fluids. In this way it can dampen the signals from the virus sensors and produce many new particles (picture, right).


Source: Linköping University

Small change in blood acidity could prove detrimental to kidney disease patients

A University of Manchester scientist has discovered that very small changes in the level of acidity in blood may have a detrimental impact on the health of patients with kidney disease.

Chronic Kidney Disease (CKD) is common in the UK.  It is estimated that about one in five men and one in four women between the ages of 65 and 74 has some degree of CKD. The leading single cause of CKD is diabetes which is increasing so it’s expected that more patients will be diagnosed with CKD in the future.

Dr Donald Ward from the Faculty of Life Sciences has been studying the impact of kidney disease on the body. He has found that very small changes in the pH (acidity) level in the blood prevents the body from being able to accurately monitor calcium levels. This leads to too much of the hormone PTH being released which is likely to lead to a greater risk of calcium and phosphate from the bone damaging the arteries. This often proves fatal to patients with CKD. His research has been published in the Journal of the American Society of Nephrology. 

Dr Donald Ward

He says: “It was not realised before that the blood pH changes we see in patients with kidney disease can have an impact on their ability to monitor blood calcium levels. My research has demonstrated that the effect of those changes may be more significant than previously thought and thus might need to be looked at more carefully by clinicians.”

Dr Ward’s research focussed on the high level of parathyroid hormone (PTH) in patients suffering from CKD. This causes the body to release calcium and phosphate from the bones which can then damage their blood vessels. 

Dr Ward explains why this is so harmful: “The diseased kidneys prevent the body getting rid of both excess phosphate and excess acidity. So if that acidity also causes the body to release more PTH then this could compound the problem by releasing further phosphate from the bone. This vicious circle might accelerate the potentially fatal calcification of the arteries.” 

He continues: “What is so important about this research is that we have demonstrated that changes in PTH release can be prompted by very small changes in blood pH level. Before, it was assumed that only a larger change in acidity would cause problems for patients.”

The research was funded by Kidney Research UK. Elaine Davies, Director of Research Operations, from the charity says: “Donald’s work has used novel pharmacological and molecular tools in generating these new findings which increase our knowledge about the complex balance that clinicians need to consider when treating patients with CKD.”

Dr Ward is hoping to take his research to the next step, testing for therapeutic targets that could lead to better treatments for CKD.

Source: Manchester University

If trees could talk: Forest research network reveals global change effects

In addition to identifying, mapping, measuring and monitoring trees in the CTFS-ForestGEO study plots, researchers describe the relatedness of trees, track flower and seed production, collect insects, survey mammals, quantify carbon stocks and flows within the ecosystem, take soil samples and measure climate variables like rainfall and temperature. The thorough study of these plots provides insights into not only how forests are changing but also why. Credit: Beth King, STRI

Permafrost thaw drives forest loss in Canada, while drought has killed trees in Panama, southern India and Borneo. In the U.S., in Virginia, over-abundant deer eat trees before they reach maturity, while nitrogen pollution has changed soil chemistry in Canada and Panama. Continents apart, these changes have all been documented by the Smithsonian-led Center for Tropical Forest Science-Forest Global Earth Observatory, CTFS-ForestGEO, which released a new report revealing how forests are changing worldwide.

"With 107 collaborators we've published a major overview of what 59 forests in 24 countries, where we monitor nearly 6 million trees teach us about forest responses to global change," said Kristina Anderson-Teixeira, first author of the report and CTFS-ForestGEO and ecosystem ecologist based at the Smithsonian Conservation Biology Institute.

Many of the changes occurring in forests worldwide are attributable to human impacts on climate, atmospheric chemistry, land use and animal populations that are so pervasive as to warrant classification of a new geologic period in Earth's history -- the Anthropocene, the Age of Humans.

Measuring and understanding the effects of all these changes -- collectively termed "global change" -- are easier said than done. Some of the best information about these global-scale changes comes from CTFS-ForestGEO, the only network of standardized forest-monitoring sites that span the globe.

Since the censuses began at the first site on Barro Colorado Island in Panama in 1981, atmospheric carbon dioxide has increased by 16 percent. The forest sites in the network have warmed by an average of over 1 degree F (0.6 degree C) and experienced up to 30 percent changes in precipitation. Landscapes around protected sites experience deforestation.
The plot network now includes forests from Brazil to northern Canada, from Gabon to England and from Papua New Guinea to China.

In addition to identifying, mapping, measuring and monitoring trees, researchers describe the relatedness of trees, track flower and seed production, collect insects, survey mammals, quantify carbon stocks and flows within the ecosystem, take soil samples and measure climate variables like rainfall and temperature. The thorough study of these plots provides insights into not only how forests are changing but also why.

Climate change scenarios predict that most of these sites will face warmer and often drier conditions in the future -- some experiencing novel climates with no modern analogs. Forests are changing more rapidly than expected by chance alone, and shifts in species composition have been associated with environmental change. Biomass increased at many tropical sites across the network.

"It is incredibly rewarding to work with a team of forest scientists from 78 research institutions around the world, including four Smithsonian units" Anderson-Teixeira said. "CTFS-ForestGEO is a pioneer in the kind of collaborative effort it takes to understand how forests worldwide are changing."

"We look forward to using the CTFS-ForestGEO network to continue to understand how and why forests respond to change, and what this means for the climate, biodiversity conservation and human well-being," said Stuart Davies, network director.

Source: Smithsonian Tropical Research Institute

Engineers to simulate, model tornado winds, their effects on buildings

Partha Sarkar designed and built the Iowa State University Tornado Simulator a decade ago. A recent grant will support new simulator studies of tornado winds and their impacts on homes and buildings. Credit: Bob Elbert

The Iowa State University Tornado Simulator kicked up a thick and slowly spinning funnel cloud over a model of a small town, overwhelming the miniature streets, buildings and homes.

Partha Sarkar turned from the laboratory vortex and announced, "That's an EF3."

Most tornadoes (about 90 percent of them) are EF3 or less in intensity. And so Sarkar advocates that homes and buildings within tornado alley across the middle of the U.S. be designed to withstand EF3 tornadoes and their top wind speeds of 165 mph.

Sarkar, an Iowa State professor of aerospace engineering, knows something about the biggest tornadoes. He walked the debris fields of Parkersburg in 2008 and Joplin, Missouri, in 2010, and has seen what the 200-plus mph winds of EF5 storms can do to cities, buildings and people.

To study the interaction of tornadoes with human-made structures, he designed and built a tornado simulator that can create and move a tornado-like vortex back and forth over a test bed. He, his coworkers and Iowa State students have worked with the simulator for a decade, studying the loads and pressures caused by laboratory storms passing over models of homes and buildings.

But, Sarkar said, there's still a lot engineers don't understand about tornado winds:

How, for example, do nearby structures and terrain affect those winds? How do building codes, building ages, structure shapes, roof types and even construction quality influence tornado damage? How do internal pressures inside buildings influence tornado damage? And, how are the wind loads distributed and shared by a building's components, such as roof sheathing, roof trusses, walls, studs and nails?

To find these answers, the National Science Foundation has awarded a pair of three-year, $250,000 collaborative research grants to Sarkar and to Texas Tech University researchers Daan Liang, an associate professor of construction engineering and engineering technology, and Xinzhong Chen, an associate professor of civil and environmental engineering.

As part of this new project, "We will try to quantify the uncertainties in estimating tornado winds and the corresponding structural damage," Sarkar said.

To do that, Sarkar said his research group will use the latest advances in tornado simulation, data acquisition and computer modeling to answer engineering questions about tornado winds and their effects on buildings.

One result of this research could be refinements to the Enhanced Fujita (EF) Scale that considers storm damage to measure the strength of tornadoes. Another result could be new provisions in building codes and construction practices for tornado-resistant buildings.

"The overarching goal of this research is to enhance society's resiliency to tornadoes through innovative design and construction of building components and systems in tornado-prone regions," the Iowa State and Texas Tech researchers wrote in a project summary.

At Iowa State, Sarkar said the grant will support experiments and data collection with the tornado simulator. One experiment, for example, will study actual buildings damaged in tornadoes by creating computer and physical models of the buildings and their structural failures. The computer models will be refined and verified by running lab tornadoes over the physical models. The computational models -- called finite element models -- will help researchers understand and predict the damage caused by tornado winds.

Data from the experiments and models will also be shared with the Texas Tech construction engineers who will study building performance in tornado winds.

"In the long run," the researchers wrote in their summary, "the research is expected to contribute to methods and strategies that can be implemented for preventing tornado hazards from becoming disasters."

Source: Iowa State University

Intensity of hurricanes: New study helps improve predictions of storm intensity

Rough sea with big waves (stock image). "The air-water interface -- whether it had significant waves or significant spray -- is a big factor in storm intensity," said Alex Soloviev, Ph.D., a professor at Nova Southeastern University's Oceanographic Center. "Hurricanes gain heat energy through the interface and they lose mechanical energy at the interface." Credit: © mimadeo / Fotolia

They are something we take very seriously in Florida -- hurricanes. The names roll off the tongue like a list of villains -- Andrew, Charlie, Frances and Wilma.

In the past 25 years or so, experts have gradually been improving prediction of the course a storm may take. This is thanks to tremendous advancements in computer and satellite technology. While we still have the "cone of uncertainty" we've become familiar with watching television weather reports, today's models are more accurate than they used to be.

The one area, however, where there is still much more to be researched and learned is in predicting just how intense a storm may be. While hurricane hunter aircraft can help determine wind speed, velocity, water temperature and other data, the fact is we often don't know why or how a storm gets stronger or weaker. There has been virtually no progress in hurricane intensity forecasting during the last quarter century.

But, thanks to new research being conducted, all that's about to change.

"The air-water interface -- whether it had significant waves or significant spray -- is a big factor in storm intensity," said Alex Soloviev, Ph.D., a professor at Nova Southeastern University's Oceanographic Center. "Hurricanes gain heat energy through the interface and they lose mechanical energy at the interface."

Soloviev is also an Adjunct Professor at the University of Miami Rosenstiel School of Marine and Atmospheric Science (UM RSMAS) and a Fellow at the Cooperative Institute for Marine and Atmospheric Studies (CIMAS.) He and his fellow researchers used a computational fluid dynamics model to simulate microstructure of the air-sea interface under hurricane force winds. In order to verify these computer-generated results, the group conducted experiments at the UM's Rosenstiel School Air-Sea Interaction Salt Water Tank (ASIST) where they simulated wind speed and ocean surface conditions found during hurricanes.

The study "The Air-Sea Interface and Surface Stress Under Tropical Cyclones" was published in the June 16, 2014 issue of the journal Nature Scientific Reports. Soloviev was the lead author of this study, which was conducted by a multi-institutional team including Roger Lukas (University of Hawaii), Mark Donelan and Brian Haus (UM RSMAS), and Isaac Ginis (University of Rhode Island.)

The researchers were surprised at what they found. Under hurricane force wind, the air-water interface was producing projectiles fragmenting into sub millimeter scale water droplets. This process is known from some engineering applications, including rocket science, as the Kelvin-Helmholtz (KH) instability. This new study then looked at how changes in microphysics of the air-sea interface can make a storm grow or weaken in intensity. With wind speed exceeding a Category 1 threshold, the ocean surface unexpectedly became more "slippery."

When the wind exceeded Category 3 hurricane force, the "slippery" effect started gradually disappearing and was completely gone at Category 5. The conclusion was that some hurricanes might rapidly intensify to Category 3 and then stay in a "comfortable" zone around Category 3 status. This finding is consistent with the global best-track tropical cyclone statistics on maximum intensity for 1982-2009. So far, these early results showed that physical conditions where the air and the ocean interact must be a vital part of any successful hurricane forecasting model and would help explain, and predict, how a storm might intensify as it moves through across the water based on the physical stress at the ocean's surface.

This work has been supported by the NOPP project "Advanced coupled atmosphere-wave-ocean modeling for improving tropical cyclone prediction models" (PIs: Isaac Ginis, URI and Shuyi Chen, UM) and by the Gulf of Mexico Research Initiative (GoMRI) Consortium for Advanced Research on the Transport of Hydrocarbons in the Environment -- CARTHE (PI: Tamay Özgökmen, UM). GoMRI is a 10-year, $500 million independent research program established by an agreement between BP and the Gulf of Mexico Alliance.

The plan is for the team to continue their research and experiments at UM's Alfred C. 

Glassell, Jr. SUSTAIN facility, which has recently been designed by one of the Nature article co-authors, Brian Haus (UM). It's the unique lab facility where they can recreate the conditions found in a Category 5 storm.

"We've got more work to do, but this is a great first step," Soloviev said. "But remember, no matter how good we get in predicting a storm's intensity, people in the path need to prepare accordingly regardless of what Category it is -- that's most important."

Source: Nova Southeastern University

Subtle shifts in the Earth could forecast earthquakes, tsunamis

University of South Florida graduate student Denis Voytenko prepares a GPS unit for a high-precision geodetic measurement.
Credit: Jacob Richardson

Earthquakes and tsunamis can be giant disasters no one sees coming, but now an international team of scientists led by a University of South Florida professor has found that subtle shifts in Earth's offshore plates can be a harbinger of the size of the disaster.

In a new paper published in the Proceedings of the National Academy of Sciences, USF geologist Tim Dixon and the team report that a geological phenomenon called "slow slip events" identified just 15 years ago is a useful tool in identifying the precursors to major earthquakes and the resulting tsunamis. The scientists used high precision GPS to measure the slight shifts on a fault line in Costa Rica, and say better monitoring of these small events can lead to better understanding of maximum earthquake size and tsunami risk.

"Giant earthquakes and tsunamis in the last decade -- Sumatra in 2004 and Japan in 2011 -- are a reminder that our ability to forecast these destructive events is painfully weak," Dixon said.

Dixon was involved in the development of high precision GPS for geophysical applications, and has been making GPS measurements in Costa Rica since 1988, in collaboration with scientists at Observatorio Vulcanológico y Sismológico de Costa Rica, the University of California-Santa Cruz, and Georgia Tech. The project is funded by the National Science Foundation.

Slow slip events have some similarities to earthquakes (caused by motion on faults) but release their energy slowly, over weeks or months, and cannot be felt or even recorded by conventional seismographs, Dixon said. Their discovery in 2001 by Canadian scientist Herb Dragert at the Pacific Geoscience Center had to await the development of high precision GPS, which is capable of measuring subtle movements of the Earth.

The scientists studied the Sept. 5, 2012 earthquake on the Costa Rica subduction plate boundary, as well as motions of the Earth in the previous decade. High precision GPS recorded numerous slow slip events in the decade leading up to the 2012 earthquake. The scientists made their measurements from a peninsula overlying the shallow portion of a megathrust fault in northwest Costa Rica.

The 7.6-magnitude quake was one of the strongest earthquakes ever to hit the Central American nation and unleased more than 1,600 aftershocks. Marino Protti, one of the authors of the paper and a resident of Costa Rica, has spent more than two decades warning local populations of the likelihood of a major earthquake in their area and recommending enhanced building codes.

A tsunami warning was issued after the quake, but only a small tsunami occurred. The group's finding shed some light on why: slow slip events in the offshore region in the decade leading up to the earthquake may have released much of the stress and strain that would normally occur on the offshore fault.

While the group's findings suggest that slow slip events have limited value in knowing exactly when an earthquake and tsunami will strike, they suggest that these events provide critical hazard assessment information by delineating rupture area and the magnitude and tsunami potential of future earthquakes.

The scientists recommend monitoring slow slip events in order to provide accurate forecasts of earthquake magnitude and tsunami potential.

Source: University of South Florida (USF Health)

This image shows a panda eating in China's Wolong Nature Reserve. Pandas habitat choices center around the ready availability of bamboo -- lots of bamboo. Credit: Sue Nichols, Michigan State University

Walter Dodds, university distinguished professor of biology (pictured), and Allison Veach, doctoral student in biology, are researching grassland streams and the expansion of nearby woody vegetation. They have studied 25 years of data on the Konza Prairie Biological Station and found that increasing fire frequency reduces the rate of woody vegetation expansion. Credit: Image courtesy of Kansas State University

Two Kansas State University biologists are studying streams to prevent tallgrass prairies from turning into shrublands and forests.

By looking at 25 years of data on the Konza Prairie Biological Station, Allison Veach, doctoral student in biology, Muncie, Indiana, and Walter Dodds, university distinguished professor of biology, are researching grassland streams and the expansion of nearby woody vegetation, such as trees and shrubs. They have found that burn intervals may predict the rate of woody vegetation expansion along streams.

Their latest research appears in the peer-reviewed journal PLOS ONE in an article "Fire and Grazing Influences on Rates of Riparian Woody Plant Expansion along Grassland Streams."

Grasslands in North America and across the globe are rapidly disappearing, Veach said, and woody plants are expanding and converting grasslands into forest ecosystems. This change in environment can affect stream hydrology and biogeochemistry, said Dodds, who has studied streams and watersheds on the Konza prairie for more than 20 years.

"This is an important issue regionally, because as trees expand into these grassland areas, people who are using grassland for cattle production have less grass for animals, too," Dodds said.

In their latest research, the biologists studied 25 years of aerial photography on Konza and observed the expansion of trees and shrubs in riparian areas, which include areas within 30 meters of streambeds. The researchers focused on three factors that affect grassland streams: burn intervals; grazers, such as bison; and the historical presence of woody vegetation.

Their analysis revealed an important finding: Burn intervals predicted the rate of woody vegetation expansion. Burning every one to two years slowed the growth of trees and shrubs, Veach said.

"Although we can reduce woody expansion by burning more frequently, we can't prevent it from occurring over time," Veach said. "Woody plant encroachment may not be prevented by fire alone."

The research shows the importance of burning to maintain the tallgrass prairie, Dodds said. While burning can help to slow the expansion of trees and shrubs, additional actions are need to maintain quickly disappearing grassland ecosystems.

"It's clear from this research that if you don't burn at all, these grassland streams basically are going to switch to forests and will not be grassland streams anymore," Dodds said.

Dodds and Veach also found that bison do not significantly affect woody vegetation expansion along streams. Previous Konza research has shown that bison do not spend significant time near stream areas, so they may not influence the growth of nearby trees and shrubs, Veach said.

Woody vegetation also may be expanding in grasslands because of more carbon dioxide in the atmosphere, Dodds said. Grasses and trees compete for carbon dioxide, and grasses are much better at conserving water and efficiently using carbon dioxide. As atmospheric carbon dioxide levels increase, it becomes easier for trees to gather carbon dioxide and gives them a growing advantage over grasses.

"The tallgrass prairie is almost nonexistent on the globe," Veach said. "In order for us to preserve tallgrass prairie, we need to look at woody encroachment because it has been an issue. Things like no fire or differences in climate change may allow woody plant species to competitively take over grasslands."

The biologists plan to continue studying water quality and quantity issues at Konza. Konza is an 8,600-acre tallgrass prairie ecological research site jointly owned by the university and The Nature Conservancy.

Source:  Kansas State University

Logging destabilizes forest soil carbon over time

Chelsea Petrenko, a doctoral candidate at Dartmouth College, is lead author of a study showing that logging triggers the gradual release of the carbon stored in a forest's mineral soils. Credit: Dartmouth College

Logging doesn't immediately jettison carbon stored in a forest's mineral soils into the atmosphere but triggers a gradual release that may contribute to climate change over decades, a Dartmouth College study finds.

The results are the first evidence of a regional trend of lower carbon pools in soils of harvested hardwood forests compared to mature or pristine hardwood forests. The findings appear in the journal Global Change Biology Bioenergy. A PDF of the study is available on request.

Despite scientists' growing appreciation for soil's role in the global carbon cycle, mineral soil carbon pools are largely understudied and previous studies have produced differing results about logging's impact. For example, the U.S. Forest Service assumes that all soil carbon pools do not change after timber harvesting.

The Dartmouth researchers looked at how timber harvesting affects mineral soil carbon over 100 years following harvest in the northeastern United States, where soils account for at least 50 percent of total ecosystem carbon storage. Mineral soils, which underlie the carbon-rich organic layer of the soil, make up the majority of that storage, but are sometimes not included in carbon studies due to the difficulty in collecting samples from the rocky, difficult terrain. The researchers hypothesized that the mineral soil carbon would be lower in forests that had been harvested in the last century than in forests that were more than 100 years old. They collected mineral soil cores from 20 forests in seven areas across the northeastern United States and compared the relative amounts of carbon in the soil from forests that were logged five years ago, 25 years ago, 50 years ago, 75 years ago and 100 years ago.

The results showed no significant differences between mineral soil carbon in the older versus harvested forests. But there was a significant relationship between the time since forest harvest and the size of the carbon pools, which suggested a gradual decline in carbon across the region that may last for decades after harvesting and result in increased atmospheric carbon dioxide.

"Our study suggests that forest harvest does cause biogeochemical changes in mineral soil, but that a small change in a carbon pool may be difficult to detect when comparing large, variable carbon pools," says lead author Chelsea Petrenko) (formerly Vario), a doctoral candidate in the Graduate Program in Ecology and Evolutionary Biology and a trainee in Dartmouth's IGERT program for Polar Environmental Change. "Our results are consistent with previous studies that found that soil carbon pools have a gradual and slow response to \disturbance, which may last for several decades following harvest."

A previous Dartmouth study found that clear-cutting releases detectible amounts of carbon stored in deep forest soils, challenging the notion that burning woody biomass for energy is more carbon-neutral than fossil fuels. "Mineral soil, which is the most significant ecosystem carbon pool in temperate forests, should be studied more closely before the carbon neutrality of bioenergy from local wood in temperate forests is asserted," says Petrenko, whose research focuses on the biogeochemistry of warming ecosystems and the impact on climate change.

Source:  Dartmouth College

Glimpsing pathway of sunlight to electricity

Andrew H. Marcus and Mark C. Lonergan stand by UO spectroscopy equipment. Credit: Image courtesy of University of Oregon

Four pulses of laser light on nanoparticle photocells in a University of Oregon spectroscopy experiment has opened a window on how captured sunlight can be converted into electricity.

The work, which potentially could inspire devices with improved efficiency in solar energy conversion, was performed on photocells that used lead-sulfide quantum dots as photoactive semiconductor material. The research is detailed in a paper placed online by the journal Nature Communications.

In the process studied, each single photon, or particle of sunlight, that is absorbed potentially creates multiple packets of energy called excitons. These packets can subsequently generate multiple free electrons that generate electricity in a process known as multiple exciton generation (MEG). In most solar cells, each absorbed photon creates just one potential free electron.

Multiple exciton generation is of interests because it can lead to solar cells that generate more electrical current and make them more efficient. The UO work shines new light on the little understood process of MEG in nanomaterials.

While the potential importance of MEG in solar energy conversion is under debate by scientists, the UO spectroscopy experiment -- adapted in a collaboration with scientists at Sweden's Lund University -- should be useful for studying many other processes in photovoltaic nanomaterials, said Andrew H. Marcus, professor of physical chemistry and head of the UO Department of Chemistry and Biochemistry.

Spectroscopic experiments previously designed by Marcus to perform two-dimensional fluorescence spectroscopy of biological molecules were adapted to also measure photocurrent. "Spectroscopy is all about light and molecules and what they do together," Marcus said. "It is a really great probe that helps to tell us about the reaction pathway that connects the beginning of a chemical or physical process to its end.

"The approach is similar to looking at how molecules come together in DNA, but instead we looked at interactions within semiconductor materials," said Marcus, an affiliate in UO's Institute of Molecular Biology, Materials Science Institute and Oregon Center for Optics. "Our method made it possible to look at electronic pathways involved in creating multiple excitons. The existence of this phenomenon had only been inferred through indirect evidence. We believe we have seen the initial steps that lead to MEG-mediated photo conductivity."

The controlled sequencing of laser pulses allowed the seven-member research team to see -- in femtoseconds (a femtosecond is one millionth of one billionth of a second) -- the arrival of light, its interaction with resting electrons and the subsequent conversion into multiple excitons. The combined use of photocurrent and fluorescence two-dimensional spectroscopy, Marcus said, provided complementary information about the reaction pathway.

UO co-author Mark C. Lonergan, professor of physical and materials chemistry, who studies electrical and electrochemical phenomena in solid-state systems, likened the processes being observed to people moving through a corn maze that has one entrance and three exits.
People entering the maze are photons. Those who exit quickly represent absorbed photons that generate unusable heat. People leaving the second exit represent other absorbed photons that generate fluorescence but not usable free electrons. People leaving the final exit signify usable electrical current.

"The question we are interested in is exactly what does the maze look like," Lonergan said. "The problem is we don't have good techniques to look inside the maze to discover the possible pathways through it. The techniques that Andy has developed basically allow us to see into the maze by encoding what is coming out of the system in terms of exactly what is going in. We can visualize what is going on, whether two people coming into the maze shook hands at some point and details about the pathway that led them to come out the electricity exit."

The project began when Tonu Pullerits, who studies ultrafast photochemistry in semiconductor molecular materials at Lund University, approached Marcus about adopting his spectroscopic system to look at solar materials. Khadga J. Karki, a postdoctoral researcher in Pullerits' lab, then visited the UO and teamed with the Marcus and Lonergan groups to reconfigure the equipment.

UO doctoral student Julia R. Widom was a co-leading author on the paper. Other co-authors with Pullerits, Marcus and Lonergan were Joachim Seibt of Lund University and UO graduate student Ian Moody.

Source:  University of Oregon

Desert streams: Deceptively simple

Dryland channels exhibit very simple topography despite being shaped by volatile rainstorms. Credit: Katerina Michaelides

Volatile rainstorms drive complex landscape changes in deserts, particularly in dryland channels, which are shaped by flash flooding. Paradoxically, such desert streams have surprisingly simple topography with smooth, straight and symmetrical form that until now has defied explanation.

That paradox has been resolved in newly published research conducted by Michael Singer and Katerina Michaelides, associate researchers at UC Santa Barbara's Earth Research Institute. The pair show that simple topography in dryland channels is maintained by complex interactions among rainstorms, the stream flows these storms generate in the river channel and sediment grains present on the riverbed. Their findings appear in the journal Geology.

Desert streams flow only during infrequent but intense rainstorms, and when they do, only parts of the channel contain water, making the flow irregular and erratic. One rainstorm may erode sediment grains in one section of the channel, while another storm moves sediment in a different area.

"Given this localized sediment movement during rainstorms, one might expect desert channels to contain mounds of sediment that undulate down the stream course reflecting the irregular flow, but they don't," Singer said. "The water produced in the channel only flows partially down the stream and then stops because it seeps into the riverbed, and there's not enough water from upstream to replace it, so it just disappears."

Because desert river channels do not feature the river bars, pools or riffles common in perennial streams, they decline in elevation downstream very smoothly. According to the researchers' findings, feedback between two variables -- complex water and sediment movements -- shape such basins.

Singer and Michaelides used data collected from the Rambla de Nogalte in southeastern Spain to model these dryland channel variables. The area has a semi-arid climate with mean annual rainfall of around 14 inches, which occurs during convective rainstorms, producing large floods that recur about once a decade.

They found that dryland channel width fluctuates downstream. Their observations show that grain size (roughness) also fluctuates from sand to gravel a downstream direction.

"There's feedback between this fluctuating width and fluctuating grain size," Singer said. "The stream flow is generated in a discontinuous pattern along the channel. Some rainstorms produce a bit of topography in some parts of the channel. Other spatial configurations of flow generated by storms destroy that topography so the variability of the rainstorms interacting with this channel are creating and destroying the topography constantly to keep it in this simple form."

Singer and Michaelides also produced simulations of extreme flows to determine the volume of flow necessary to reshape the channel completely. They examined the longitudinal variability of sediment flow as well as sediment storage to find the channel-shaping threshold. This threshold reshapes the entire channel and makes it smooth again. "It's a really significant threshold that tells us the magnitude of the flood necessary to reshape the channel," Singer said.

"Semi-arid and arid river systems are extremely important to the populations that live around them," he concluded. "Water resources are obviously a huge limitation in the development of societies, and a lot of water is being progressively diverted for irrigation, water use and other purposes, so those can further affect the spatial patterns of where flow is in these channels and potentially impact the processes of where topography develops in the river channel. Humans can inadvertently have an impact on the shape and form of river channels like these."

Source:  University of California - Santa Barbara