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Australian Geographic: Secrets of leaf size revealed

New findings reveal the real reasons behind varying leaf sizes.

Australian Geographic has covered the research of SMU paleobotanist Bonnie F. Jacobs, a professor in SMU’s Roy M. Huffington Department of Earth Sciences.

Working with a global team of researchers, Jacobs and her colleagues cracked the mystery of leaf size. The research was published Sept. 1, 2017 as a cover story in Science.

The researchers from Australia, the U.K., Canada, Argentina, the United States, Estonia, Spain and China analyzed leaves from more than 7,600 species of plants over the past 20 years, then pooled and analyzed the data with new theory to create a series of equations that can predict the maximum viable leaf size anywhere in the world based on the risk of daytime overheating and night-time freezing.

The researchers will use these findings to create more accurate vegetation models. This will be used by governments to predict how vegetation will change locally and globally under climate change, and to plan for adaptation.

Jacobs contributed an extensive leaf database — research that was funded by a National Science Foundation grant. She analyzed the leaf characteristics of 880 species of modern tropical African plants, which occurred in various combinations among 30 plant communities. Jacobs measured leaves of the plant specimens at the Missouri Botanical Garden Herbarium, one of the largest archives of pressed dried plant specimens from around the world.

Jacobs is one of a handful of the world’s experts on the fossil plants of ancient Africa. As part of a team of paleontologists working there, she hunts plant and animal fossils in Ethiopia’s prolific Mush Valley, as well as elsewhere in Africa.

Read the full story.

EXCERPT:

By Karl Gruber
Australian Geographic

You may have learnt at school that leaf size depends on water availability and that they are meant to help plants avoid overheating. But a new study that looked at leaf sizes around the world found that, rather than water availability, it all boils down to temperature, both high and low.

Leaf sizes can vary by as much as 100,000 fold, with some leaves having an area of just 1 mm2 while other can have an area of up to 1 m2. But what is driving these big differences?

“The conventional explanation was that water availability and overheating were the two major limits to leaf size. But the data didn’t fit,” says Ian. “For example the tropics are both wet and hot, and leaves in cooler parts of the world are unlikely to overheat,” explained Ian Wright, from Macquarie University, who led the new study.

A key finding from the study is that for plants all around the world the main factors limiting leaf size are the risk of frosting in cold nights, which can damage leaves, and the risk of overheating during the day.

“Latitude explains 28% of variation leaf size, globally. Warm wet regions are characterised by large-leaved species, warm dry regions and cold regions by smaller-leaved species. These patterns can all be understood in relation to the energy inputs and outputs to leaves, but only if you consider both the daytime (overheating) and night-time (freezing) risks,” Wright says.

Read the full story.

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Earth & Climate Fossils & Ruins Plants & Animals Researcher news SMU In The News

BBC: Clues to why leaves come in many sizes

The huge variety of leaves in the plant kingdom has long been a source of wonder and fascination.

BBC News has covered the research of SMU paleobotanist Bonnie F. Jacobs, a professor in SMU’s Roy M. Huffington Department of Earth Sciences.

Working with a global team of researchers, Jacobs and her colleagues cracked the mystery of leaf size. The research was published Sept. 1, 2017 as a cover story in Science.

The researchers from Australia, the U.K., Canada, Argentina, the United States, Estonia, Spain and China analyzed leaves from more than 7,600 species of plants over the past 20 years, then pooled and analyzed the data with new theory to create a series of equations that can predict the maximum viable leaf size anywhere in the world based on the risk of daytime overheating and night-time freezing.

The researchers will use these findings to create more accurate vegetation models. This will be used by governments to predict how vegetation will change locally and globally under climate change, and to plan for adaptation.

Jacobs contributed an extensive leaf database — research that was funded by a National Science Foundation grant. She analyzed the leaf characteristics of 880 species of modern tropical African plants, which occurred in various combinations among 30 plant communities. Jacobs measured leaves of the plant specimens at the Missouri Botanical Garden Herbarium, one of the largest archives of pressed dried plant specimens from around the world.

Jacobs is one of a handful of the world’s experts on the fossil plants of ancient Africa. As part of a team of paleontologists working there, she hunts plant and animal fossils in Ethiopia’s prolific Mush Valley, as well as elsewhere in Africa.

Read the full story.

EXCERPT:

By Helen Briggs
BBC News

The leaves of a banana plant, for instance, are about a million times bigger than the leaves of heather.

The conventional wisdom is that leaf size is limited by the balance between how much water is available to a plant and the risk of overheating.

However, a study of more than 7,000 plant species around the world suggests the answer may be more complex.

“A banana leaf is able to be so huge because bananas naturally grow in places that are very hot and very wet,” said Ian Wright of Macquarie University in Sydney, Australia.
“Our work shows that in fact that if there’s enough water in the soil then there’s almost no limit to how large leaves can be.”

He says this is only part of the puzzle of leaf size.

“The other part is about the tendency for larger leaves to freeze at night,” Dr Wright explained.

“And, you put these two ingredients together — the risk of freezing and the risk of overheating — and this helps understand the pattern of leaf sizes you see across the entire world.”

There are hundreds of thousands of plant species on the planet, from tiny alpine plants to massive jungle palms.

Their leaves vary in area from less than 1 square millimetre to greater than 1 square metre.

Large-leaved plants predominate in tropical jungle — something that was noted as early as the 19th Century. Meanwhile, small-leaved plants thrive in arid deserts and at high latitudes.

Some decades ago, scientists realised that variability in leaf size was related to water and temperature. They proposed that the limit to leaf size was set by the risk of overheating.

Thus, when rainfall is high, plants can get away with having larger leaves.
The new research, published in the journal Science, suggests this idea applies only in certain regions of the globe.

“There were some pieces in this puzzle that were clearly missing,” Dr. Wright told BBC News.

Read the full story.

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The mystery of leaf size solved by global team of scientists

A global team of researchers, including SMU paleobotanist Bonnie Jacobs, have cracked the mystery of leaf size. The research was published Sept. 1, 2017 as a cover story in Science.

SMU paleobotanist Bonnie F. Jacobs has contributed research to a major new study that provides scientists with a new tool for understanding both ancient and future climate by looking at the size of plant leaves.

Why is a banana leaf a million times bigger than a common heather leaf? Why are leaves generally much larger in tropical jungles than in temperate forests and deserts? The textbooks say it’s a balance between water availability and overheating.

But it’s not that simple, the researchers found.

The study, published in the Sept. 1, 2017 issue of Science, was led by Associate Professor Ian Wright from Macquarie University, Australia. The study’s findings reveal that in much of the world the key factor limiting the size of a plant’s leaves is the temperature at night and the risk of frost damage to leaves.

Jacobs said the implications of the study are significant for enabling scientists to either predict modern leaf size in the distant future, or to understand the climate for a locality as it may have been in the past.

“This research provides scientists with another tool for predicting future changes in vegetation, given climate change, and for describing ancient climate given fossil leaves,” said Jacobs, a professor in SMU’s Roy M. Huffington Department of Earth Sciences in the Dedman College of Humanities and Sciences.

“Now we can reliably use this as another way to look at future climate models for a specific location and predict the size of plant leaves,” she said. “Or, if we’re trying to understand what the climate was for a prehistoric site tens of millions of years ago, we can look at the plant fossils discovered in that location and describe what the climate most likely was at that time.”

Wright, Jacobs and 15 colleagues from Australia, the U.K., Canada, Argentina, the United States, Estonia, Spain and China analyzed leaves from more than 7,600 species, then pooled and analyzed the data with new theory to create a series of equations that can predict the maximum viable leaf size anywhere in the world based on the risk of daytime overheating and night-time freezing.

The researchers will use these findings to create more accurate vegetation models. This will be used by governments to predict how vegetation will change locally and globally under climate change, and to plan for adaptation.

Big data solves century-old conundrum
The iconic paintings of Henri Rousseau illustrate that when we think of steamy tropics we expect large leaves. But for scientists it’s been a century-old conundrum: why does leaf size vary with latitude – from very small near the poles to massive leaves in the tropics?

“The conventional explanation was that water availability and overheating were the two major limits to leaf size. But the data didn’t fit,” says Wright. “For example the tropics are both wet and hot, and leaves in cooler parts of the world are unlikely to overheat.”

“Our team worked both ends of the problem – observation and theory,” he says. “We used big data – measurements made on tens of thousands of leaves. By sampling across all continents, climate zones and plant types we were able to show that simple ‘rules’ seemingly operate across the world’s plant species, rules that were not apparent from previous, more limited analyses.”

Jacobs contributed an extensive leaf database she compiled about 20 years ago, funded by a National Science Foundation grant. She analyzed the leaf characteristics of 880 species of modern tropical African plants, which occurred in various combinations among 30 plant communities. Jacobs measured leaves of the plant specimens at the Missouri Botanical Garden Herbarium, one of the largest archives of pressed dried plant specimens from around the world.

She looked at all aspects of leaf shape and climate, ranging from seasonal and annual rainfall and temperature for each locale, as well as leaf shape, size, tip, base, among others. Using statistical analyses to plot the variables, she found the most prominent relationship between leaf shape and climate was that size increases with rainfall amount. Wet sites had species with larger leaves than dry sites.

Her Africa database was added to those of many other scientists who have compiled similar data for other localities around the world.

Threat of night time frost damage determines the size of a leaf
“Using our knowledge of plant function and biophysics we developed a fresh take on ‘leaf energy balance’ theory, and compared our predictions to observed leaf sizes,” Wright says.

“The most surprising result was that over much of the world the maximum size of leaves is set not by the risk of overheating, but rather by the risk of damaging frost at night. Larger leaves have thicker, insulating ‘boundary layers’ of still air that slows their ability to draw heat from their surroundings – heat that is needed to compensate for longwave energy lost to the night-time sky,” says co-author Colin Prentice from Imperial College London, who co-ordinated the mathematical modelling effort.

“International collaborations are making ecology into a predictive science at global scale,” says Emeritus Professor Mark Westoby. “At Macquarie University we’re proud to have led this networking over the past 20 years.” — Margaret Allen, SMU, and Macquarie University

By Ian Wright
Macquarie University

As a plant ecologist, I try to understand variation in plant traits (the physical, chemical and physiological properties of their tissues) and how this variation affects plant function in different ecosystems.

For this study I worked with 16 colleagues from Australia, the UK, Canada, Argentina, the US, Estonia, Spain and China to analyse leaves from more than 7,600 species. We then teamed the data with new theory to create a model that can predict the maximum viable leaf size anywhere in the world, based on the dual risks of daytime overheating and night-time freezing.

These findings will be used to improve global vegetation models, which are used to predict how vegetation will change under climate change, and also to better understand past climates from leaf fossils.

From giants to dwarfs
The world’s plant species vary enormously in the typical size of their leaves; from 1 square millimetre in desert species such as common eutaxia (Eutaxia microphylla), or in common heather (Calluna vulgaris) in Europe, to as much as 1 square metre in tropical species like Musa textilis, the Filipino banana tree.

But what is the physiological or ecological significance of all this variation in leaf size? How does it affect the way that plants “do business”, using leaves as protein-rich factories that trade water (transpiration) for carbon (photosynthesis), powered by energy from the sun?

More than a century ago, early plant ecologists such as Eugenius Warming argued that it was the high rainfall in the tropics that allowed large-leaved species to flourish there.

In the 1960s and ‘70s physicists and physiologists tackled the problem, showing that in mid-summer large leaves are more prone to overheating, requiring higher rates of “transpirational cooling” (a process akin to sweating) to avoid damage. This explained why many desert species have small leaves, and why species growing in cool, shaded understoreys (below the tree canopy) can have large leaves.

But still there were missing pieces to this puzzle. For example, the tropics are both wet and hot, and these theories predicted disadvantages for large-leafed species in hot regions. And, in any case, overheating must surely be unlikely for leaves in many cooler parts of the world.

Our research aimed to find these missing pieces. By collecting samples from all continents, climate zones and plant types, our team found simple “rules” that appear to apply to all of the world’s plant species – rules that were not apparent from previous, more limited analyses.

We found the key factors are day and night temperatures, rainfall and solar radiation (largely determined by distance from the Equator and the amount of cloud cover). The interaction of these factors means that in hot and sunny regions that are also very dry, most species have small leaves, but in hot or sunny regions that receive high rainfall, many species have large leaves. Finally, in very cold regions (e.g. at high elevation, or at high northern latitudes), most species have small leaves.

But the most surprising results emerged from teaming the new theory for leaf size, leaf temperature and water use with the global data analyses, to investigate what sets the maximum size of leaves possible at any point on the globe.

Read the author’s full essay

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A Total Eclipse of the First Day of School

Dedman College, SMU Physics Department host Great American Solar Eclipse 2017 viewing

Thousands of students, faculty and townspeople showed up to campus Monday, Aug. 21 to observe the Great American Solar Eclipse at a viewing hosted by Dedman College of Humanities and Sciences and the SMU Department of Physics.

The festive event coincided with the kick-off of SMU’s Fall Semester and included Solar Eclipse Cookies served while viewing the rare astronomical phenomenon.

The eclipse reached its peak at 1:09 p.m. in Dallas at more than 75% of totality.

“What a great first day of the semester and terrific event to bring everyone together with the help of Dedman College scientists,” said Dedman Dean Thomas DiPiero. “And the eclipse cookies weren’t bad, either.”

Physics faculty provided indirect methods for observing the eclipse, including a telescope with a viewing cone on the steps of historic Dallas Hall, a projection of the eclipse onto a screen into Dallas Hall, and a variety of homemade hand-held devices.

Outside on the steps of Dallas Hall, Associate Professor Stephen Sekula manned his home-built viewing tunnel attached to a telescope for people to indirectly view the eclipse.

“I was overwhelmed by the incredible response of the students, faculty and community,” Sekula said. “The people who flocked to Dallas Hall were energized and engaged. It moved me that they were so interested in — and, in some cases, had their perspective on the universe altered by — a partial eclipse of the sun by the moon.”

A team of Physics Department faculty assembled components to use a mirror to project the eclipse from a telescope on the steps of Dallas Hall into the rotunda onto a screen hanging from the second-floor balcony.

Adjunct Professor John Cotton built the mount for the mirror — with a spare, just in case — and Professor and Department Chairman Ryszard Stroynowski and Sekula arranged the tripod setup and tested the equipment.

Stroynowski also projected an illustration of the Earth, the moon and the sun onto the wall of the rotunda to help people visualize movement and location of those cosmic bodies during the solar eclipse.

Professor Fred Olness handed out cardboard projectors and showed people how to use them to indirectly view the eclipse.

“The turn-out was fantastic,” Olness said. “Many families with children participated, and we distributed cardboard with pinholes so they could project the eclipse onto the sidewalk. It was rewarding that they were enthused by the science.”

Stroynowski, Sekula and others at the viewing event were interviewed by CBS 11 TV journalist Robert Flagg.

Physics Professor Thomas Coan and Guillermo Vasquez, SMU Linux and research computing support specialist, put together a sequence of photos they took during the day from Fondren Science Building.

“The experience of bringing faculty, students and even some out-of-campus community members together by sharing goggles, cameras, and now pictures of one of the great natural events, was extremely gratifying,” Vasquez said.

Sekula said the enthusiastic response from the public is driving plans to prepare for the next event of this kind.

“I’m really excited to share with SMU and Dallas in a total eclipse of the sun on April 8, 2024,” he said.

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Texas Tribune: The Q&A — Dr. Diego Román, Simmons School

In this week’s Q&A, The Texas Tribune interviews Diego Román, assistant professor of teaching and learning at Southern Methodist University.

Texas Tribune reporter Cassandra Pollock interviewed SMU education expert Diego Román in the Annette Caldwell Simmons School of Education and Human Development for a Q&A about how middle school science textbooks frame climate change as an opinion rather than scientific fact.

Román is co-author of a 2015 study of California 6th grade science textbooks and how they present global warming.

Studies estimate that only 3 percent of scientists who are experts in climate analysis disagree about the role of humans in the causes of climate change. And the most recent report from the Intergovernmental Panel on Climate Change — the evidence of 600 climate researchers in 32 countries reporting changes to Earth’s atmosphere, ice and seas — in 2013 stated “human influence on the climate system is clear.”

Yet only 54 percent of American teens believe climate change is happening, 43 percent don’t believe it’s caused by humans, and 57 percent aren’t concerned about it.

The new study measured how four sixth-grade science textbooks adopted for use in California frame the subject of global warming. Sixth grade is the first time California state standards indicate students will encounter climate change in their formal science curriculum.

“We found that climate change is presented as a controversial debate stemming from differing opinions,” said Román, an assistant professor in the Department of Teaching and Learning. “Climate skeptics and climate deniers are given equal time and treated with equal weight as scientists and scientific facts — even though scientists who refute global warming total a miniscule number.”

The findings were reported in October 2015 at the 11th Conference of the European Science Education Research Association (ESERA), held in Helsinki, Finland.

The findings were also published in the Environmental Education Research journal in the article, “Textbooks of doubt: Using systemic functional analysis to explore the framing of climate change in middle-school science textbooks.”

The Texas Tribune article, “The Q&A: Diego Román,” published Aug. 17, 2017.

Read the full story.

EXCERPT:

By Cassandra Pollock
Texas Tribune

With each issue, Tasbo+Edu brings you an interview with experts on issues related to health care. Here is this week’s subject:

Diego Román is an assistant professor in teaching and learning at Southern Methodist University. He has recently researched how climate change is framed for middle school students in science textbooks.

Tasbo+Edu: Can you briefly explain your research findings?

Dr. Diego Román: The big picture of my research is that I look at the linguistic and social factors that impact language use in the science-education context and language development for English learners who are attending school in the U.S.

I am an applied linguist, and one of my research topics was the framing of climate change in middle school textbooks. In terms of the science textbooks and what we found in that specific study, the ones we investigated don’t reflect the way scientists discuss climate change in reports. While science reports resort to the certainty that climate change is happening, the textbooks that we looked at were very uncertain about defining that issue. We looked into seeing why that would be the case, particularly at how science is seen as very specific, objective and certain, but when we discuss climate change, we use a lot of qualifiers — “would,” “could” and “might.”

We’re arguing that this places the weight on the reader to decipher what that means. “Not all” could mean 90 percent, 55 percent or 10 percent, depending on who you’re talking to. So while textbooks are required to address certain topics — such as climate change — they’re not using specific language to help students and teachers have a better understanding and discussion around the issue.

I also look at how we use language — and I do that by using a framework called systemic functional linguistics. It argues that language is caused by the context of use, so the way we talk about science and the way we frame science topics when discussing them may be different than social studies. To explain a different type of knowledge, we connect ideas differently. For example, we emphasize the idea versus the people in science, but in social studies, we look at the people. To do that, we use language. So I look at how language is used in those purposes to convey knowledge and be effective. I try to understand the perspectives of the authors or the people. That’s a big picture description of my research.

Tasbo+Edu: What are the biggest challenges you see moving forward to try to modify the textbook system?

Román: It seems to be how research can impact, in this case, textbook development, and how to find things that applied linguists are doing when it relates to how language is used and if there’s a way to convey scientific knowledge — from a contextual perspective, but also from a linguistics perspective.

Read the full story.