“We found that trees in warmer, drier climates are essentially coughing instead of breathing,” said Max Lloyd assistant research professor of geosciences at Penn State and lead author on the study recently published in Proceedings of the National Academy of Sciences. “They are sending CO₂ right back into the atmosphere far more than trees in cooler, wetter conditions.”

Through the process of photosynthesis, trees remove CO₂ from the atmosphere to produce new growth. Yet, under stressful conditions, trees release CO₂ back to the atmosphere, a process called photorespiration. With an analysis of a global dataset of tree tissue, the research team demonstrated that the rate of photorespiration is up to two times higher in warmer climates, especially when water is limited. They found the threshold for this response in subtropical climates begins to be crossed when average daytime temperatures exceed roughly 68 degrees Fahrenheit and worsens as temperatures rise further.

The results complicate a widespread belief about the role of plants in helping to draw down, or use, carbon from the atmosphere, providing new insight into how plants could adapt to climate change. Importantly, the researchers noted that as the climate warms, their findings demonstrate that plants could be less able to draw CO₂ out of the atmosphere and assimilate the carbon necessary to help the planet cool down.

“We have knocked this essential cycle off balance,” Lloyd said. “Plants and climate are inextricably linked. The biggest draw down of CO₂ from our atmosphere is photosynthesizing organisms. It’s a big knob on the composition of the atmosphere, so that means small changes have a large impact.”

Plants currently absorb an estimated 25% of the CO₂ emitted by human activities each year, according to the U.S. Department of Energy, but this percentage is likely to decrease in the future as the climate warms, Lloyd explained, especially if water is scarcer.

“When we think about climate futures, we predict that CO₂ will go up, which in theory is good for plants because those are the molecules they breathe in,” Lloyd said. “But we’ve shown there will be a tradeoff that some prevailing models don’t account for. The world will be getting warmer, which means plants will be less able to draw down that CO₂.”

In the study, the researchers discovered that variation in the abundance of certain isotopes of a part of wood called methoxyl groups serves as a tracer of photorespiration in trees. You can think of isotopes as varieties of atoms, Lloyd explained. Just as you might have vanilla and chocolate versions of ice cream, atoms can have different isotopes with their own unique “flavors” due to variations in their mass. The team studied levels of the methoxyl “flavor” of isotope in wood samples from about thirty specimens of trees from a variety of climates and conditions throughout the world to observe trends in photorespiration. The specimens came from an archive at the University of California, Berkeley, that contains hundreds of wood samples collected in the 1930s and 40s.

“The database was originally used to train foresters how to identify trees from different places around the world, so we repurposed it to essentially reconstruct these forests to see how well they were taking in CO₂,” Lloyd said.

Until now, photorespiration rates could only be measured in real time using living plants or well-preserved dead specimens that retained structural carbohydrates, which meant that it was nearly impossible to study the rate at which plants draw down carbon at scale or in the past, Lloyd explained.

Now that the team has validated a way to observe photorespiration rate using wood, he said the method could offer researchers a tool for predicting the how well trees might “breathe” in future and how they fared in past climates.

The amount of carbon dioxide in the atmosphere is rapidly rising; it is already greater than at any time in the last 3.6 million years, according to the National Oceanic and Atmospheric Administration. But that period is relatively recent in geologic time, Lloyd explained.

The team will now work to unearth photorespiration rates in the ancient past, up to tens of millions of years ago, using fossilized wood. The methods will allow researchers to explicitly test existing hypotheses regarding the changing influence of plant photorespiration on climate over geologic time.

“I’m a geologist, I work in the past,” Lloyd said. “So, if we’re interested in these big questions about how this cycle worked when the climate was very different than today, we can’t use living plants. We may have to go back millions of years to better understand what our future might look like.”

Other authors on the paper are Rebekah A. Stein, Daniel A. Stolper, Daniel E. Ibarra and Todd E. Dawson of the University of California, Berkeley; Richard S. Barclay and Scott L. Wing of the Smithsonian National Museum of Natural History and David W. Stahle of the University of Arkansas.

The work was funded in part by the Agouron Institute, the Heising-Simons Foundation, and the U.S. National Science Foundation.

Africa’s Greater Virunga Landscape (GVL) is a 15,700-square-kilometer area of savannas, mountains and lakes in Uganda, Rwanda and the Democratic Republic of Congo. It is home to the largest land animals in Africa, with seven national parks, three tropical high-forest reserves and three wildlife reserves, three of which are world heritage sites, covering 88% of the area. It is also home to a population of African elephants whose numbers have dropped so precipitously over the past century that they are now listed as critically endangered by the International Union for Conservation’s Red List.

Elephants play a key role in modifying and sustaining their landscapes by dispersing the seeds of the plants they feed upon, felling trees and enriching soil fertility with their dung. They also play an important role in many African cultures.

To date, few studies have focused on the dynamics of the environment, climate change, elephant demography and how the changing habitat influences elephants over long periods. To get a clearer picture of what the elephants’ future might look like and what we can do to best ensure their survival, lead author Simon Nampindo, who completed this research as part of his Ph.D. in environmental conservation for UMass Amherst and who is now country director for WCS Uganda, and Timothy Randhir, professor of environmental conservation at UMass Amherst, built a systems dynamic model. “This model,” says Nampindo, “can look at all the different environmental and population dynamics within a system. For the first time, we’re able to get a comprehensive vision of what the future might look like for African elephants in the face of climate change.”

Nampindo and Randhir built their model using data on the numbers of elephants, historical changes in the landscape and different future climate-change scenarios representing 1.6 º, 2.8º and 4.3º Celsius of warming over the next 80 years. Finally, they charted the effect each of the climate scenarios would have on five elephant age brackets: under 10 years old, 11 — 30, 31 — 40, 41 — 50, and more than 50 years old, because, as Randhir puts it “any impact on one age class has a community effect throughout the entire population.”

“We found that the older elephants will be massively affected by warming under every scenario,” says Nampindo. “Elephants are matriarchal — their leaders are the older cows, and the herds depend on their wisdom, long memories and ability to outsmart prey, and if they are lost to changing climate, it will wreak havoc on the surviving, younger herds, as well as change the genetic profiles and structures of the herd. There will also be ripple effects through the GVL’s landscape.”

“But,” says Randhir, “this model not only tells us what the threats are, we can also use it to tell us which policy possibilities will be most effective in helping African elephants to survive.”

In the case of a species like the elephant, which migrates widely across national boundaries, it is especially important to also understand how differing policies could affect future herds so that management agencies can coordinate their responses.

In particular, Nampindo and Randhir find that a coordinated GVL management strategy at the national, regional and local levels is needed to address poaching threats. Well-funded anti-poaching efforts are essential, but they also point to the importance of community-led programs and education in the front-line towns and villages where human-elephant interaction is common. The GVL landscape must also be managed appropriately to reduce the impact of habitat fragmentation, fire and invasive species.

“These results are very important to WCS,” says Nampindo. “If we can do a good job at protecting elephants, our efforts will reverberate to other species, such as lions and mountain gorillas.”

“More broadly,” says Randhir, “the most exciting thing about this systems dynamic modeling is that it can be adapted to any migratory species that move across political boundaries, from fish to birds to lions.”

Radon is a naturally occurring radioactive gas produced when metals like uranium or radium break down in rocks and soil. The gas can make its way into homes through cracks in basement walls and floors, construction joints and gaps around pipes.

“Radon is an indoor air pollutant that can only be detected through testing that measures concentrations of the gas in homes,” said study author Eric A. Whitsel, MD, MPH, of the University of North Carolina in Chapel Hill. “Our research found an increased risk of stroke among participants exposed to radon above — and as many as two picocuries per liter (pCi/L) below — concentrations that usually trigger Environmental Protection Agency recommendations to install a home radon mitigation system.”

The study involved 158,910 female participants with an average age of 63 who did not have stroke at the start of the study. They were followed for an average of 13 years. During the study, there were 6,979 strokes among participants.

To determine radon exposures, researchers linked participants’ home addresses to radon concentration data from the U.S. Geological Survey and the U.S. Environmental Protection Agency (EPA).

The EPA recommends that average indoor radon concentrations do not exceed four picocuries per liter (pCi/L). For concentrations this high, the EPA recommends installing a radon mitigation system to lower radon levels in the home.

Participants were divided into three groups. The highest group had homes in areas where average radon concentrations were more than four pCi/L. The middle group lived in areas with average concentrations between two and four pCi/L. The lowest group lived in areas with average concentrations of less than two pCi/L.

In the group with the highest radon exposures, there were 349 strokes per 100,000 person-years compared to 343 strokes in the middle group and 333 strokes in group with the lowest exposure. Person-years represent both the number of people in the study and the amount of time each person spends in the study.

After adjusting for factors such as smoking, diabetes and high blood pressure, researchers found participants in the highest group had a 14% increased risk of stroke compared to those in the lowest group. Those in the middle group had a 6% increased risk.

“It’s important to note that we found an increased stroke risk among those exposed to radon concentrations as much as two pCi/L below the current lung cancer-based threshold for recommending radon mitigation,” said Whitsel. “More studies are needed to confirm our findings. Confirmation would present an opportunity to improve public health by addressing an emerging risk factor for stroke.”

A limitation of the study was that it included only female participants who were middle age or older and primarily white, so the results may not be the same for other populations.

The study was funded by the National Institute of Environmental Health Sciences and National Heart, Lung, and Blood Institute.