Thursday, June 17, 2021

Sorghum, a close relative of corn, tested for disease resistance on Pennsylvania farms

PENN STATE

With sorghum poised to become an important crop grown by Pennsylvania farmers, Penn State researchers, in a new study, tested more than 150 germplasm lines of the plant for resistance to a fungus likely to hamper its production.

Sorghum, a close relative to corn, is valuable for yielding human food, animal feed and biofuels. Perhaps its most notable attribute is that the grain it produces is gluten free. Drought resistant and needing a smaller amount of nutrients than corn to thrive, sorghum seems to be a crop that would do well in the Keystone State's climate in a warming world. But its susceptibility to fungal disease is problematic.

"In other locations where sorghum has been grown for a long time, it is attacked by a fungal pathogen that causes a disease called anthracnose leaf blight, which diminishes its yield," said study co-author Surinder Chopra, professor of maize genetics in the College of Agricultural Sciences. "We conducted a three-part experiment designed to evaluate the likelihood that anthracnose will be a problem with sorghum production in Pennsylvania, and what plants might resist the disease."

First, researchers carried out field surveys in 2011, 2012 and 2016 in six Pennsylvania locations to monitor the presence of the Colletotrichum fungus that causes anthracnose in commercial sorghum fields. They collected soil samples, plant samples and samples of the debris left by sorghum or corn, looking for the fungus at sites in Blair, Lancaster, Dauphin, Centre, Bedford and Lebanon counties.

Next, researchers grew 158 sorghum lines at Penn State's Russell E. Larson Agricultural Research Center at Rock Springs and tested them for vulnerability and resistance to the natural strains of anthracnose fungus. They obtained plant material for many of the sorghum lines from the International Crops Research Institute for the Semi-Arid Tropics, better known as ICRISAT, India.

Other sorghum lines came from varieties Chopra's research group has been breeding in plots at Rock Springs for years and are being tested for stress tolerance in another study. Still others came from sources such as the U.S. Department of Agriculture's Agricultural Research Service stations in Griffin, Georgia, Lincoln, Nebraska, and Lubbock, Texas; the Grain, Forage and Bioenergy Research Center, Texas A&M Agrilife Sorghum Breeding Program; and the National Plant Germplasm System.

Lastly, researchers conducted experiments in greenhouses on the University Park campus. They chose 35 sorghum lines that demonstrated resistance to the fungus in field trials and tested their responses after inoculating them with the pathogen. The team evaluated and scored those plants for the severity of anthracnose leaf blight that developed.

In findings recently published in Crop Science, Chopra and colleagues reported that the anthracnose leaf blight symptoms were observed on the older and senescent leaves in Pennsylvania. After evaluating, in field and greenhouse tests, the performance of the 158 experimental lines and commercial hybrids, the researchers noted that they discovered sources of resistance to anthracnose leaf blight.

"Many of those sorghum lines we tested had been improved in several states in the U.S. and in other parts of the world," Chopra said. "These should be useful in breeding programs targeted for Pennsylvania and for northeastern U.S. climatic conditions. Several lines received from ICRISAT showed the high level of resistance in the field."

The research was done in preparation for widespread cultivation of sorghum in Pennsylvania, at which time anthracnose leaf blight is expected to become a problem for farmers, Chopra explained.

"Our study is the first to investigate the frequency, diversity and distribution of Colletotrichum fungi species on sorghum in Pennsylvania, and the first to look for disease-tolerant strains that will grow best in the Northeast," he said. "Our findings will help develop better recommendations for sorghum growers so they can manage and proactively prevent the buildup of inoculum and resulting disease outbreaks."

Also involved in the research were Iffa Gaffoor, former postdoctoral scholar in the Department of Plant Science at Penn State, advised by Chopra; Germán Sandoya, Everglades Research and Education Center/Horticultural Sciences Department, University of Florida; Katia Xavier, Lisa Vaillancourt and Etta Nuckles, Department of Plant Pathology, University of Kentucky; and Srinivasa R Pinnamaneni, Sorghum Breeding Program, ICRISAT, Patancheru, India.

The U.S. Department of Agriculture's National Institute of Food and Agriculture and the Fundacion Alfonso Martin Escudero for postdoctoral research provided funding for this work.

CAPTION

Sorghum, a close relative to corn, is valuable for yielding human food, animal feed and biofuels. Perhaps its most notable attribute is that the grain it produces is gluten free.

CREDIT

Surinder Chopra, Penn State

CAPTION

Researchers cultured Colletotrichum strains recovered from sorghum from various Pennsylvania farms (top and middle rows). Spores (bottom row) were collected from the culture plates at 14 days after inoculation.

CREDIT

Chopra Lab, Penn State

LA REVUE GAUCHE - Left Comment: Search results for SORGHUM

Women in science propose changes to discriminatory measures of scientific success

SMITHSONIAN TROPICAL RESEARCH INSTITUTE

Research News

IMAGE: ANA K. SPALDING AND 23 OTHER WOMEN SCIENTISTS FROM AROUND THE WORLD, ADVOCATE FOR A SHIFT IN THE VALUE SYSTEM IN SCIENCE, TO EMPHASIZE A MORE EQUAL, DIVERSE AND INCLUSIVE... view more
CREDIT: JORGE ALEMAN

When Ana K. Spalding, a Research Associate at the Smithsonian Tropical Research Institute (STRI) and Assistant Professor of Marine and Coastal Policy at Oregon State University (OSU) talks about mentorship in academia, she describes it as meaningful relationship. It goes beyond conversations about research and publications, and into shared experiences. This is just one approach--proposed by Spalding and 23 other women scientists from around the world, in a new article published in PLOS Biology--that calls for a shift in the value system of science to emphasize a more equal, diverse and inclusive academic culture.

The authors came together after reading a paper in Nature Communications that was later retracted, which claimed that women in science fare better with male rather than female mentors. That paper used data on co-authorship among senior and junior researchers and citations as measures of mentorship and success. Yet these metrics are flawed and biased against marginalized groups. The data show that women receive more manuscript rejections and are less likely to be published in prestigious journals than men, while ethnically diverse scientific teams experience lower acceptance rates and fewer citations than less diverse teams.

Meanwhile, productivity is not always a sign of a supportive working environment, and recent studies show that graduate students are twice as likely to experience mental health challenges, compared to the general population with equivalent education. For women of color in STEMM fields, the trend is even more pronounced. They face both systemic sexism and racism, along with daily microaggressions. The situation is not much better for sexual minorities.

Spalding is afro-Panamanian, and a minority among tenured faculty at OSU. According to a 2019 article in the Chronicle of Higher Education, less than 1 percent of tenured professors at OSU look like her. In the state of Oregon, things are not much different, where only about 2 percent of the population is Black or African American, per the U.S. Census Bureau. So, around OSU, challenges range from lack of representation in predominantly white spaces where her presence or expertise are questioned, to finding places to get her hair done (where hair, as a representation of Blackness is often questioned or seen as unprofessional).

As a graduate student, she never felt represented. Looking back, Spalding understands how important it would have been to have the kind of support where her identity and culture were considered holistically. In that sense, the PLOS Biology article encourages individuals to explore a variety of mentoring relationships throughout their careers: relationships that may help them achieve their different goals and needs beyond academia. This is one crucial way to promote wellbeing and foster a sense of belonging for mentees with diverse backgrounds, increasing their retention in science.

"Don't think you have to be a certain way to belong," Spalding said. "Feel confident that you belong, but also look for people who accept you as you are."

Ultimately, the authors call for the scientific community, in particular those in positions of power and privilege, to take strong action towards helping ensure safe and healthy work environments for scientists from diverse backgrounds, while supporting a more inclusive value system in science that embraces the multifaceted nature of scientific impact. With these changes in place, the scientific world will not only have a greater capacity for innovation, which is essential for addressing the pressing challenges of our times, such as pandemics and climate change, but will be a better place from a purely humanistic perspective.

As an example, Katalin Kariko, a Hungarian scientist who immigrated to the United States, struggled to find a permanent position for decades, relying instead on senior scientists to take her in. Now, her groundbreaking research in mRNA has made possible the development of the Pfizer-BioNTech and Moderna vaccines against Covid-19.

"I'm particularly excited about the idea of expanding our definitions of science to be more inclusive of applied and relevant contributions to societal issues such as climate change (which may or may not get into the highest impact journals)," said Spalding. "Furthermore, I am keen on supporting a 'multidimensional mentorship model' that emphasizes mentee wellbeing in academia."

CAPTION

The proposed multidimensional mentorship model goes beyond conversations about research and publications, and into shared experiences. This image is from a dig in Cambutal, Panama, led by STRI archaeologists Ashley Sharpe and Nicole Smith-Guzman who hosted a class of students from the United States and Panama.

CREDIT

Ana Endara

The Smithsonian Tropical Research Institute, headquartered in Panama City, Panama, is part of the Smithsonian Institution. The Institute furthers the understanding of tropical nature and its importance to human welfare, trains students to conduct research in the tropics and promotes conservation by increasing public awareness of the beauty and importance of tropical ecosystems.

Mountain fires burning higher at unprecedented rates

Climate change to blame for making high-elevation forests particularly susceptible to blazes

MCGILL UNIVERSITY

Research News

Forest fires have crept higher up mountains over the past few decades, scorching areas previously too wet to burn, according to researchers from McGill University. As wildfires advance uphill, a staggering 11% of all Western U.S. forests are now at risk.

"Climate change and drought conditions in the West are drying out high-elevation forests, making them particularly susceptible to blazes," says lead author Mohammad Reza Alizadeh, a PhD student at McGill University under the supervision of Professor Jan Adamowski. "This creates new dangers for mountain communities, with impacts on downstream water supplies and the plants and wildlife that call these forests home."

Climate warming has diminished 'flammability barrier'

In a study published in Proceedings of the National Academy of Sciences, the researchers analyzed records of fires larger than 405 hectares in the mountainous regions of the contiguous Western U.S. between 1984 and 2017. Their results show that climate warming has diminished the 'high-elevation flammability barrier' - the point where forests historically were too wet to burn regularly because of the lingering presence of snow. The researchers found that fires advanced about 252 meters uphill in the Western mountains over those three decades.

The amount of land that burned increased across all elevations during that period, however the largest increase was at elevations above 2,500 meters. Additionally, the area burning above 8,200 feet more than tripled in 2001 to 2017 compared with 1984 to 2000. Over the past 34 years, rising temperatures have extended fire territory in the West to an additional 81,500 square kilometers of high-elevation forests, an area similar in size to South Carolina.

"Climate change continues to increase the risk of fire, and this trend will likely continue as the planet warms. More fire activity higher in the mountains is yet another warning of the dangers that lie ahead," says co-author Jan Adamowski, a Professor in the Department of Bioresource Engineering at McGill University.

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About this study

"Warming enabled upslope advance in western US forest fires" by Mohammad Reza Alizadeh, John T. Abatzoglou, Charles H. Luce, Jan F. Adamowski, Arvin Farid, and Mojtaba Sadegh was published on June 1, 2021 in in Proceedings of the National Academy of Sciences.

DOI: https://doi.org/10.1073/pnas.2009717118

Managed retreat: A must in the war against climate change

New research finds that moving off the coast and away from floods can expand options

UNIVERSITY OF DELAWARE

VIDEO: NEW RESEARCH FROM THE UNIVERSITY OF DELAWARE'S A.R. SIDERS AND KATHARINE MACH, FROM THE UNIVERSITY OF MIAMI, FOUND THAT MANAGED RETREAT CAN'T BE SEEN AS A LAST RESORT -- IT... view more

CREDIT: JEFFREY C. CHASE/ UNIVERSITY OF DELAWARE

University of Delaware disaster researcher A.R. Siders said it's time to put all the options on the table when it comes to discussing climate change adaptation.

Managed retreat -- the purposeful movement of people, buildings and other assets from areas vulnerable to hazards -- has often been considered a last resort. But Siders said it can be a powerful tool for expanding the range of possible solutions to cope with rising sea levels, flooding and other climate change effects when used proactively or in combination with other measures.

Siders, a core faculty member in UD's Disaster Research Center, and Katharine J. Mach, associate professor at the University of Miami Rosenstiel School of Marine and Atmospheric Science, provide a prospective roadmap for reconceptualizing the future using managed retreat in a new paper published online in Science on June 17, 2021.

"Climate change is affecting people all over the world, and everyone is trying to figure out what to do about it. One potential strategy, moving away from hazards, could be very effective, but it often gets overlooked," said Siders, assistant professor in the Joseph R. Biden, Jr. School of Public Policy and Administration and the Department of Geography and Spatial Sciences. "We are looking at the different ways society can dream bigger when planning for climate change and how community values and priorities play a role in that."

Retreat does not mean defeat

Managed retreat has been happening for decades all over the United States at a very small scale with state and/or federal support. Siders pointed to Hurricanes Harvey and Florence as weather events that caused homeowners near the Gulf of Mexico to seek government support for relocation. Locally, towns such as Bowers Beach, near the Delaware coast, have used buyouts to remove homes and families from flood-prone areas, an idea that Southbridge in Wilmington is also exploring.

People often oppose the idea of leaving their homes, but Siders said thinking seriously about managed retreat sooner and in context with other available tools can reinforce decisions by prompting difficult conversations. Even if communities decide to stay in place, identifying the things community members value can help them decide what they want to maintain and what they purposely want to change.

"If the only tools you think about are beach nourishment and building walls, you're limiting what you can do, but if you start adding in the whole toolkit and combining the options in different ways, you can create a much wider range of futures," she said.

In the paper, Siders and Mach argue that long-term adaptation will involve retreat. Even traditionally accepted visions of the future, like building flood walls and elevating threatened structures, will involve small-scale retreat to make space for levees and drainage. Larger-scale retreat may be needed for more ambitious transformations, such as building floating neighborhoods or cities, turning roads into canals in an effort to live with the water, or building more dense, more compact cities on higher ground.

Some, but not all these futures currently exist.

In the Netherlands, the municipality of Rotterdam has installed floating homes in Nassau harbor that move with the tides, providing a sustainable waterfront view for homeowners while making room for public-friendly green space along the water. In New York City, one idea under consideration is building into the East River to accommodate a floodwall. Both cities are using combination strategies that leverage more than one adaptation tool.

Adaptation decisions don't have to be either/or decisions. However, it is important to remember that these efforts take time, so planning should begin now.

"Communities, towns, and cities are making decisions now that affect the future," said Siders. "Locally, Delaware is building faster inside the floodplain than outside of it. We are making plans for beach nourishment and where to build seawalls. We're making these decisions now, so we should be considering all the options on the table now, not just the ones that keep people in place."

According to Siders, the paper is a conversation starter for researchers, policymakers, communities and residents that are invested in helping communities thrive amid changing climate. These discussions, she said, shouldn't focus solely on where we need to move from, but also where we should avoid building, where new building should be encouraged, and how we should build differently.

"Managed retreat can be more effective in reducing risk, in ways that are socially equitable and economically efficient, if it is a proactive component of climate-driven transformations," said Mach. "It can be used to address climate risks, along with other types of responses like building seawalls or limiting new development in hazard-prone regions."

Globally, Siders said the U.S. is in a privileged position, in terms of the available space, money and resources, relative to other countries facing more complicated futures. The Republic of Kiribati, a chain of islands in the central Pacific Ocean, for example, is expected to be under water in the future. Some of its islands already are uninhabitable.

The Kiribati government has bought land in Fiji for relocation and is developing programs with Australia and New Zealand to provide skilled workforce training so the Kiribati people can migrate with dignity when the time comes. Challenges remain, though, since not everyone is on board with moving.

In a recent special issue of the Journal of Environmental Studies and Sciences, edited and introduced by Siders and Idowu (Jola) Ajibade at Portland State University, researchers examined the social justice implications of managed retreat in examples from several countries, including the U.S., Marshall Islands, New Zealand, Peru, Sweden, Taiwan, Austria and England. The scientists explored how retreat affects groups of people and, in the U.S., specifically considered how retreat affects marginalized populations.

So, how can society do better? According to Siders, it starts with longer-term thinking.

"It's hard to make good decisions about climate change if we are thinking 5-10 years out," said Siders. "We are building infrastructure that lasts 50-100 years; our planning scale should be equally long."

Siders will give a keynote address and research presentation on the topic at a virtual managed retreat conference at Columbia University, June 22-25, 2021.

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Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.

THE COMMONWEALTH IS SACRED

Sacred natural sites protect biodiversity in Iran

Research team from the Universities of Kassel, Göttingen and Kurdistan investigate this form of local nature conservation

UNIVERSITY OF GÖTTINGEN

Research News

IMAGE: HOW MUCH DO TRADITIONAL PRACTICES CONTRIBUTE TO THE PROTECTION OF LOCAL BIODIVERSITY? WHY AND HOW ARE SACRED GROVES LOCALLY VALUED AND PROTECTED, AND HOW CAN THIS BE PROMOTED AND HARNESSED... view more
CREDIT: ZAHED SHAKERI

How much do traditional practices contribute to the protection of local biodiversity? Why and how are sacred groves locally valued and protected, and how can this be promoted and harnessed for environmental protection? Working together with the University of Kurdistan, researchers of the University of Göttingen and the University of Kassel have examined the backgrounds of this form of local environmental protection in Baneh County, Iran.

"Around the world, local communities are voluntarily protecting certain parts of their surroundings due to religious reasons - be it in Ethiopia, Morocco, Italy, China or India", reports Professor Tobias Plieninger, head of the section Social-ecological Interactions in Agricultural Systems at the universities of Kassel and Göttingen. Sacred natural sites are places where traditional myths and stories meet local ecological knowledge and environmental protection. Beyond state-based protection programs, these form a network of informal nature reserves.

In the contested border areas between Iran and Iraq, state-run environmental protection programs are often failing, while natural resources are under a lot of pressure. Even in such areas of conflict, patches of highly biodiverse woodlands still exist thanks to informal conservation traditions - in the form of decades-old sacred natural sites, some of which are known as the 'sacred groves'.

In the Middle East, sacred groves are quite common, but there has been very little research into these biocultural hotspots. They usually belong to a Mosque and serve as village cemeteries, the use of which is strictly regulated. Even though they usually cover only a small area - 1 hectare on average - they are comparatively rich in biodiversity, provide numerous ecosystem services and are of great cultural and spiritual importance to local communities.

Local people regard them as the abodes of their ancestors. Dr Zahed Shakeri, who accompanied the project as a post-doc researcher and grew up in the region himself, reports on the numerous myths and legends that surround these sites and demand a careful maintenance as well as respectful behavior. "Our research group developed a fascination for the botanical treasures of these sites," Plieninger tells. In a vegetation study, they found out that the taxonomic diversity in sacred groves is much higher than in neighboring cultivated lands. The vegetation composition, too, is fundamentally different here.

"The 22 sacred groves examined comprised 20% of the flora of the whole region. Moreover, they host multiple rare and endangered plants, and represent complex niches for threatened animals", Shakeri reports. "Due to this taxonomic diversity, sacred groves can serve as an important complement to formally protected areas in the region, and as baselines in their reconstruction." Today, due to changes in customary rights, population growth and the loss of traditional faiths, the number and condition of such sacred natural sites are decreasing around the world. Thus, local people's perceptions regarding sacred groves as well as the reasons for their relatively good condition in the region were also subject of this research.

On the basis of interviews with 205 residents from 25 villages, the research group identified people's key motivations for the areas' protection: in particular spiritual values, the preservation of cultural and spiritual heritage as well as of local biodiversity played a role here. Furthermore, the importance of taboos became clear, which particularly prohibit the use of natural resources (for instance forest clearance, hunting and livestock grazing) and road construction, but also regulate the general behavior within these sites.

Even though these social values and taboos are considered relatively stable in the province of Kurdistan, the interviewees repeatedly referred to the threatened situation of the groves in the region. Especially elderly and rural people, women and people with traditional lifestyles were regarded as the holders of these values and taboos. "Protection programs could support these groups to defend and revive their customs. At the same time, young and urban people with modern lifestyles represent an important target group for awareness-raising," Shakeri summarizes.

The example of sacred groves demonstrates that social dynamics and especially cultural values deserve greater attention in environmental protection: "Such a biocultural approach to conservation that considers different worldviews and knowledge systems, could translate social taboos and the related land-use practices into socially acceptable and environmentally effective conservation outcomes", Plieninger concludes.

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On the online blog of the research group Social-Ecological Interactions in Agricultural Systems: https://medium.com/people-nature-landscapes

The (English-language) blog articles:
Sacred Groves in Kurdistan: Biodiversity, Locally Preserved
Sacred Groves as a Safe Shelter for Biodiversity and Culture in Kurdistan

Original publications:Plieninger, T., Quintas-Soriano, C., Torralba, M., Muhammadi Sammani, K., & Shakeri, Z. 2020.Social dynamics of values, taboos and perceived threats around sacred groves in Kurdistan, Iran. People and Nature 2: 1237-1250 AND
Shakeri, Z., Mohammadi-Samani, K., Bergmeier, E. & Plieninger, T. 2021. Spiritual values shape taxonomic diversity, vegetation composition, and conservation status in woodlands of the Northern Zagros, Iran. Ecology and Society 26, art. 30.
https://doi.org/10.5751/ES-12290-260130

Excess nitrogen puts butterflies at risk

UNIVERSITY OF BASEL

Research News

IMAGE: RARE BUTTERFLIES SUCH AS THE WESTERN FRITILLARY (*MELITAEA PARTHENOIDES*) SUFFER FROM HIGH NITROGEN EMISSIONS. view more
CREDIT: TOBIAS ROTH

Nitrogen from agriculture, vehicle emissions and industry is endangering butterflies in Switzerland. The element is deposited in the soil via the air and has an impact on vegetation - to the detriment of the butterflies, as researchers at the University of Basel have discovered.

More than half of butterfly species in Switzerland are considered to be at risk or potentially at risk. Usually, the search for causes focuses on intensive agriculture, pesticide use and climate change. A research team led by Professor Valentin Amrhein from the University of Basel, however, has been investigating another factor - the depositing of nitrogen from agriculture and exhaust fumes from industry and traffic in soils via the air. In the journal Conservation Biology, the research team reports a connection between this unintentional fertilization and the low diversity of butterflies in Switzerland.

It was already known from previous studies that too much nitrogen leads to denser vegetation, but with a smaller selection of plant species. Nitrogen stimulates the growth of less demanding plants in particular, with more specialized species being displaced. "We wanted to find out whether a nitrogen surplus also indirectly affects the diversity of butterflies via this change in vegetation," explains Dr. Tobias Roth, lead author of the study.

The team analyzed data from Biodiversity Monitoring Switzerland on the diversity and prevalence of plants and butterflies on 383 plots throughout Switzerland. The result was clear: the more nitrogen introduced via the air to the areas studied, the less diverse the vegetation and hence the butterfly species.

"As caterpillars, some butterfly species need certain plant species as food, or are dependent on a certain microclimate," Roth explains. Over-fertilization results in open, warm and dry places becoming cooler, shadier and damper due to stronger plant growth.

The nitrogen surplus impacts the prevalence of a large number of butterfly species in Switzerland, such as those that prefer open and dry sites. The researchers saw the clearest effect in rare and endangered species. "Nitrogen from the air is likely to be an important factor in the reason why these species are endangered," Roth remarks.

Existing literature on the diversity of butterflies explains the presence or absence of species primarily in terms of habitat quality or climate. A literature review by the research team revealed that plant diversity and vegetation density have so far received less attention. "We believe that the impact of nitrogen enrichment on butterflies has been underestimated," says Amrhein. Nitrogen appears to play a similarly extensive role as climate change when it comes to butterfly diversity.

While the researchers do not see a simple approach for improving the situation, technical improvements continue to offer a certain potential. "In the past, slurry was sprayed on farmland, for example, and some of this was transferred to other areas of land by the wind," Roth explains. Today, he says, drag hoses are used increasingly to apply the slurry directly to the soil. This reduces nitrogen input via the air to other areas where it is not wanted.

In addition, buffer zones and adapted landscape management can also help to partially mitigate the negative impact on sensitive habitats: this includes measures to prevent scrub encroachment, such as grazing or more frequent mowing. This is beneficial not only for demanding plant species, but also for butterflies. According to the researchers, however, there is ultimately no way around environmentally friendly consumer behavior when it comes to reducing unwanted nitrogen input, for example through the reduction of vehicle emissions and livestock farming. Around two thirds of nitrogen input into sensitive ecosystems in Switzerland today originate from ammonia emissions from livestock farming.

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21ST CENTURY ALCHEMY

Tailored laser fields reveal properties of transparent crystals

Research team led by the University of Göttingen investigates surface magnetisation

UNIVERSITY OF GÖTTINGEN

Research News

IMAGE: IMAGE OF QUARTZ CRYSTALS UNDER ILLUMINATION WITH STRONG LASER FIELDS OF DIFFERENT COLOURED LIGHT (RED AND BLUE), AND BOTH COLOURS ADDED TOGETHER (MIDDLE). view more
CREDIT: MURAT SIVIS

The surface of a material often has properties that are very different from the properties within the material. For example, a non-conducting crystal, which actually exhibits no magnetism, can show magnetisation restricted to its surface because of the way the atoms are arranged there. These distinct properties at interfaces and surfaces of materials often play a key role in the development of new functional components such as optoelectronic chips or sensors and are therefore subject to extensive research. An international research team from the University of Göttingen, the Max Planck Institute for Biophysical Chemistry Göttingen and the National Research Council Canada has now succeeded in investigating the surfaces of transparent crystals using powerful irradiation from lasers. The results of the study were published in the journal Nature Communications.

The researchers describe their method, which relies purely on light, to determine electrical and magnetic properties on surfaces. This new method could play an important role in the investigation of transparent, non-conductive materials, as established methods using electrons often experience experimental limitations due to low conductivity, among other difficulties. The use of light helps get around these limitations: when light rays hit a material surface, for example a glass pane, they are reflected at the interface, refracted and absorbed into the material. These effects, which can be observed in everyday life, are the result of the interaction of the weak light field with the atoms and electrons of the irradiated material. In the case of stronger light fields, which are achieved with lasers, further effects occur, which can, for example, generate higher light frequencies - known as high harmonic radiation. These effects are often dependent on the direction of oscillation of the light field relative to the atomic arrangement in the material.

"We take advantage of this dependence when generating high harmonic radiation to gain insights into the properties at and near the surface of transparent materials," says first author and PhD student Tobias Heinrich from the Faculty of Physics at Göttingen University. "The light field we use is composed of two laser pulses rotating in opposite directions at two different frequencies, and this results in a cloverleaf-shaped symmetrical field." These tailor-made light fields can be adapted to the atomic arrangement of the material to control the generation of the high harmonics.

"We show that this control can be used to study magnetisation at the surface of magnesium oxide," explains Dr Murat Sivis, the study lead. Depending on the direction of rotation of the light field - also called chirality - the generated ultraviolet light is absorbed to different degrees at the interface. "For various materials that do not actually exhibit magnetisation or electrical conductivity, these properties at the surface have been predicted in theory," Sivis said. "In our study, we show that it is now possible to investigate such phenomena using just optical methods, probably even at very short time scales." The researchers also hope to gain new insights into the electronic properties of other chiral materials, as the study shows using the example of the helical crystal structure of quartz. The sensitivity to chiral phenomena on surfaces could potentially open up new opportunities for research into innovative functional materials.

CAPTION

Image of a quartz crystal illuminated by light made up of two colours.

CREDIT

Murat Sivis

CAPTION

Artist's impression of the illumination of a magnesium oxide crystal lattice with strong triangular symmetrical laser fields

CREDIT

Murat Sivis

Originalveröffentlichung: Tobias Heinrich et al. „Chiral high-harmonic generation and spectroscopy on solid surfaces using polarization-tailored strong fields". Nature Communications (2021).

Doi: 10.1038/s41467-021-239