• Reducing the number of stomata that rice have makes them more tolerant to salt water, according to researchers at the University of Sheffield
• As sea levels rise, seawater is reaching places it previously wouldn’t, causing increasing damage to crops
• Sheffield scientists had already discovered that rice with fewer stomata are more drought resistant, needing up to 60 per cent less water — now, they have shown that the same plants are also able to grow in salty conditions
• Rice is arguably the most important food crop on earth — it is relied on by 3.5 billion people every single day, and 30 per cent of the world’s freshwater supply is used to grow the crop

Genetically engineering rice to have better salt tolerance could allow it to be grown in places it would otherwise fail, new research from the University of Sheffield has found.

As sea levels rise as a result of climate change, more and more places around the world are struggling with seawater inundation — where salt water from the sea is flooding further inland and destroying crops which can’t cope with the increased salinity.

Rice is one of the worst affected crops — the most important carbohydrate on earth, it is relied on by 3.5 billion people every day, but in countries like Vietnam it is becoming harder and harder to grow due to increasing seawater interference.

However, findings from the University of Sheffield’s Institute for Sustainable Food have revealed that genetically modifying rice to reduce the number of stomata is has — tiny openings used for water loss — makes it more salt-resistant.

Stomata are openings that most plants have which regulate carbon dioxide uptake for photosynthesis, along with the release of water vapour. Several years ago, Sheffield scientists revealed that reducing the number and size of stomata rice plants have allows them to use up to 60 per cent less water, making them hugely beneficial in places prone to drought.

Those findings, along with these new results, published in the New Phytologist, mean that rice can be adapted to survive in environments that are becoming harsher due to climate change, which will help in tackling food insecurity around the globe.

The researchers also discovered, however, that reducing the number and size of stomata could make rice harder to grow in extremely hot temperatures. As a result, to make sure that rice can grow as effectively as possible in different countries and environments, different modifications will need to be made. For example — rice with fewer, larger stomata, could be better suited to growing in extremely warm temperatures.

Dr Robert Caine, Lead Author of the study from the University of Sheffield’s School of Biosciences, said: “Rice is a hugely important food crop eaten by over half the world’s population on a daily basis. Ensuring that it can survive in harsher conditions caused by climate change will be integral to feeding a growing population that is projected to reach 10 billion in 60 years’ time.

“Our findings reveal how rice can be modified to grow as effectively as possible in different climates — varieties of rice that have less stomata can survive with less water and in places with salt water. Meanwhile, natural rice varieties with fewer, bigger stomata are able to thrive in hotter temperatures.”

The researchers from the University of Sheffield, working alongside the High Agricultural Technology Research Institute (HATRI) in Vietnam, studied 72 rice varieties, both natural and genetically modified. They are now planning to investigate whether they can make dwarf rice varieties, which produce the highest crop yields, more heat-resistant.

A new study indicates that scientists have substantially underestimated the energy output of these objects by not recognizing the extent to which their light is dimmed by dust.

“When there are intervening small particles along our line of sight, this makes things behind them look dimmer. We see this at sunset on any clear day when the sun looks fainter,” said Martin Gaskell, a research associate in astronomy and astrophysics at UC Santa Cruz.

Gaskell is lead author of a paper on the new findings published January 16 in Monthly Notices of the Royal Astronomical Society.

Although the possibility of dust dimming the light from active galactic nuclei has been recognized for a long time, the amount was controversial and was widely believed to be negligible, he said.

“We have shown that this is not the case and that the far ultraviolet light of a typical active galactic nucleus is dimmed by a large factor,” Gaskell said.

The team reached this conclusion by studying the reddening effect of dust on the light from one of the most well-studied active galactic nuclei, known as NGC 5548. Just as the Earth’s atmosphere makes the sun appear redder as well as dimmer at sunset, so dust in active galactic nuclei also makes them appear redder than they really are. The amount of reddening is related to the amount of dimming.

Scientists quantify the colors of something by measuring the ratios of the intensity of its light at different wavelengths. While we know what the unreddened color of the sun is, there has been much debate over the unreddened colors of the various types of emission from active galactic nuclei. This is because, although simple theories predict the intrinsic, unreddened colors, there were doubts about whether these simple theories applied to active galactic nuclei.

In the new study of NGC 5548, the UCSC researchers used seven different indicators of the amount of dust and found them all to be in good agreement. Furthermore, the dimming of NGC 5548 due to dust was found to be large, more than ten times the dimming caused by dust as we look out of our own galaxy, the Milky Way.

“The good agreement between the different indicators of the amount of reddening was a pleasant surprise,” said Gaskell. “It strongly supports simple theories of emission from active galactic nuclei. Exotic explanations of colors are not needed. This makes life simpler for researchers and is speeding up our understanding of what happens as black holes swallow material.”

The colors of NGC 5548 are typical of other active galactic nuclei, he said, which has wide-ranging implications. Because of the dimming effects of dust, active galactic nuclei are even more powerful than had been realized. The results imply that in the ultraviolet, where most of the energy is radiated, a typical active galactic nucleus is putting out an order of magnitude more energy than previously thought, Gaskell said.

Another implication, he said, is that active galactic nuclei are very similar, and what had hitherto been thought to be major fundamental differences between them are really just the consequences of different amounts of reddening by dust.

Gaskell’s coauthors — Frances Anderson (now at Harvey Mudd College), Sufia Birmingham (now at Princeton University), and Samhita Ghosh (now at UC Berkeley) — worked on this project as high school seniors participating in the UCSC Science Internship Program.

Ants are ectotherms — animals whose body temperature depends on the environment. While these animals experience a range of temperatures in daily life, most ectotherms prefer habitats that are slightly cooler than the so-called optimal functioning temperature in which an ectothermic animal is able to best perform all of life’s functions. If it encounters an environment warmer than the optimal point, an ectotherm risks approaching the lethal end of its physiology’s spectrum. In other words, if it gets too hot, ectotherms will die.

Little is known, however, about how — or if — insect ectotherms will adjust their behavior to avoid warmer but sublethal temperature ranges — where functioning is physiologically possible but not optimal — which are increasingly likely due to global climate change.

To learn more about how insect species may respond to those warmer, sublethal temperatures, researchers at NC State studied five species of ants common in North Carolina. The researchers counted and collected ants in forest ecosystems and measured air temperatures at the collection sites to identify the distribution of available microhabitats. The researchers also used a unique ant thermometer to measure the temperature of the ants themselves (which varied by ant color and body size). Lastly, to determine each species’ preferred temperature, the researchers collected some ants for the lab and placed them in a rectangular chamber with a controlled temperature gradient.

The researchers found that ants in the lab did have distinct thermal preferences, but ants in the field were active in their preferred climates only slightly more often than expected by chance. Instead, most species were collected in sites that were warmer than preferred, suggesting lack of awareness or some limitation in their ability to adjust to increasing temperatures.

“It’s interesting that the worker ants we observed were willing to put themselves in uncomfortable situations while foraging,” says Sara Prado, an adjunct professor and co-author of the study. “I wonder if the food was ‘profitable’ enough for the ants to stretch their comfort levels, or if they are simply willing to sacrifice their well-being for the sake of the colony.”

“Warmer times and places make warmer ants, and they’re not adjusting their activity to match their preferred conditions,” says Elsa Youngsteadt, a professor of applied ecology at NC State and co-author of the study. “For now, this may be a tradeoff that works out fine for them. But if you think of the huge biomass of ants underfoot, their metabolic rates are all creeping upward as the climate changes. Even if it doesn’t kill them outright, what does that amped-up metabolism mean for their life cycle and even the whole forest ecosystem?”

Youngsteadt plans to further investigate this question with urban ants that are effectively living in the future of climate change in comparatively warm cities.

The paper, “Can behavior and physiology mitigate effects of warming on ectotherms? A test in urban ants,” will be published January 16 in the Journal of Animal Ecology. The paper was co-authored by Michelle Kirchner from NC State University and Kirsten Keleher from Cornell University. The work was supported by the USDA National Institute of Food and Agriculture, Hatch Project #1018689 to Youngsteadt, and by North Carolina State University.

With luminosities exceeding entire galaxies (i.e., billions of times brighter than our Sun) for brief periods of time (months to years), accretion events enable astrophysicists to study supermassive black holes (SMBHs) from cosmological distances, providing a window into the central regions of otherwise-quiescent — or dormant — galaxies. By probing these “strong-gravity” events, where Einstein’s general theory of relativity is critical for determining how matter behaves, TDEs yield information about one of the most extreme environments in the universe: the event horizon — the point of no return — of a black hole.

TDEs are usually “once-and-done” because the extreme gravitational field of the SMBH destroys the star, meaning that the SMBH fades back into darkness following the accretion flare. In some instances, however, the high-density core of the star can survive the gravitational interaction with the SMBH, allowing it to orbit the black hole more than once. Researchers call this a repeating partial TDE.

A team of physicists, including lead author Thomas Wevers, Fellow of the European Southern Observatory, and co-authors Eric Coughlin, assistant professor of physics at Syracuse University, and Dheeraj R. “DJ” Pasham, research scientist at MIT’s Kavli Institute for Astrophysics and Space Research, have proposed a model for a repeating partial TDE. Their findings, published in Astrophysical Journal Letters, describe the capture of the star by a SMBH, the stripping of the material each time the star comes close to the black hole, and the delay between when the material is stripped and when it feeds the black hole again. The team’s work is the first to develop and use a detailed model of a repeating partial TDE to explain the observations, make predictions about the orbital properties of a star in a distant galaxy, and understand the partial tidal disruption process.

The team is studying a TDE known as AT2018fyk (AT stands for “Astrophysical Transient”). The star was captured by a SMBH through an exchange process known as “Hills capture,” where the star was originally part of a binary system (two stars that orbit one another under their mutual gravitational attraction) that was ripped apart by the gravitational field of the black hole. The other (non-captured) star was ejected from the center of the galaxy at speeds comparable to ~ 1000 km/s, which is known as a hypervelocity star.

Once bound to the SMBH, the star powering the emission from AT2018fyk has been repeatedly stripped of its outer envelope each time it passes through its point of closest approach with the black hole. The stripped outer layers of the star form the bright accretion disk, which researchers can study using X-Ray and Ultraviolet /Optical telescopes that observe light from distant galaxies.

According to Wevers, having the opportunity to study a partial TDE gives unprecedented insight into the existence of supermassive black holes and the orbital dynamics of stars in the centers of galaxies.

“Until now, the assumption has been that when we see the aftermath of a close encounter between a star and a supermassive black hole, the outcome will be fatal for the star, that is, the star is completely destroyed,” he says. “But contrary to all other TDEs we know of, when we pointed our telescopes to the same location again several years later, we found that it had re-brightened again. This led us to propose that rather than being fatal, part of the star survived the initial encounter and returned to the same location to be stripped of material once more, explaining the re-brightening phase.”

First detected in 2018, AT2018fyk was initially perceived as an ordinary TDE. For approximately 600 days the source stayed bright in the X-ray, but then abruptly went dark and was undetectable — a result of the stellar remnant core returning to a black hole, explains MIT physicist Dheeraj R. Pasham.

“When the core returns to the black hole it essentially steals all the gas away from the black hole via gravity and as a result there is no matter to accrete and hence the system goes dark,” Pasham says.

It wasn’t immediately clear what caused the precipitous decline in the luminosity of AT2018fyk, because TDEs normally decay smoothly and gradually — not abruptly — in their emission. But around 600 days after the drop, the source was again found to be X-ray bright. This led the researchers to propose that the star survived its close encounter with the SMBH the first time and was in orbit about the black hole.

Using detailed modeling, the team’s findings suggest that the orbital period of the star about the black hole is roughly 1,200 days, and it takes approximately 600 days for the material that is shed from the star to return to the black hole and start accreting. Their model also constrained the size of the captured star, which they believe was about the size of the sun. As for the original binary, the team believes the two stars were extremely close to one another before being ripped apart by the black hole, likely orbiting each other every few days.

So how could a star survive its brush with death? It all comes down to a matter of proximity and trajectory. If the star collided head-on with the black hole and passed the event horizon — the threshold where the speed needed to escape the black hole surpasses the speed of light — the star would be consumed by the black hole. If the star passed very close to the black hole and crossed the so-called “tidal radius” — where the tidal force of the hole is stronger than the gravitational force that keeps the star together — it would be destroyed. In the model they have proposed, the star’s orbit reaches a point of closest approach that is just outside of the tidal radius, but doesn’t cross it completely: some of the material at the stellar surface is stripped by the black hole, but the material at its center remains intact.

How, or if, the process of the star orbiting the SMBH can occur over many repeated passages is a theoretical question that the team plans to investigate with future simulations. Syracuse physicist Eric Coughlin explains that they estimate between 1 to 10% of the mass of the star is lost each time it passes the black hole, with the large range due to uncertainty in modeling the emission from the TDE.

“If the mass loss is only at the 1% level, then we expect the star to survive for many more encounters, whereas if it is closer to 10%, the star may have already been destroyed,” notes Coughlin.

The team will keep their eyes to the sky in the coming years to test their predictions. Based on their model, they forecast that the source will abruptly disappear around March 2023 and brighten again when the freshly stripped material accretes onto the black hole in 2025.

The team says their study offers a new way forward for tracking and monitoring follow-up sources that have been detected in the past. The work also suggests a new paradigm for the origin of repeating flares from the centers of external galaxies.

“In the future, it is likely that more systems will be checked for late-time flares, especially now that this project puts forth a theoretical picture of the capture of the star through a dynamical exchange process and the ensuing repeated partial tidal disruption,” says Coughlin. “We’re hopeful this model can be used to infer the properties of distant supermassive black holes and gain an understanding of their “demographics,” being the number of black holes within a given mass range, which is otherwise difficult to achieve directly.”

The team says the model also makes several testable predictions about the tidal disruption process, and with more observations of systems like AT2018fyk, it should give insight into the physics of partial tidal disruption events and the extreme environments around supermassive black holes.

“This study outlines methodology to potentially predict the next snack times of supermassive black holes in external galaxies,” says Pasham. “If you think about it, it is pretty remarkable that we on Earth can align our telescopes to black holes millions of light years away to understand how they feed and grow.”

Additional co-authors include: M. Guolo, Department of Physics and Astronomy, Johns Hopkins University; Y. Sun, University of Arizona; S. Wen, Department of Astrophysics/IMAPP, Radboud University ; P.G. Jonker, Department of Astrophysics/IMAPP, Radboud University and SRON, Netherlands Institute for Space Research ; A. Zabludoff, University of Arizona; A. Malyali, R. Arcodia, Z. Liu, A. Merloni, A. Rau and I. Grotova, Max-Planck-Institut fu ?r extraterrestrische Physik , Germany; P. Short, Institute for Astronomy, University of Edinburgh; and Z. Cao, Department of Astrophysics/IMAPP, Radboud University

Video: https://youtu.be/_TRtPDbaQ2k