PLANT FOSSILS AND OUR WORLD'S PAST

FROM:  NATIONAL SCIENCE FOUNDATION 

Tiny plant fossils offer window into Earth's landscape millions of years ago
Fossilized plant pieces tell a detailed story of our planet 50 million years ago
Minuscule, fossilized pieces of plants tell a detailed story of what Earth looked like 50 million years ago.

Researchers have discovered a way of determining density of trees, shrubs and bushes in locations over time--based on clues in the cells of plant fossils preserved in rocks and soil.

Tree density directly affects precipitation, erosion, animal behavior and a host of other factors in the natural world. Quantifying vegetation structure throughout time could shed light on how Earth's ecosystems have changed over millions of years.

"Knowing an area's vegetation structure and the arrangement of leaves on the Earth's surface is key to understanding the terrestrial ecosystem," says Regan Dunn, a paleontologist at the University of Washington's Burke Museum of Natural History and Culture. "It's the context in which all land-based organisms live, but we didn't have a way to measure it until now."

The findings are published in this week's issue of the journal Science.

New method offers window into distant past

"The new methodology provides a high-resolution lens for viewing the structure of ecosystems over the deep history of our planet," says Alan Tessier, acting director of the National Science Foundation's (NSF) Division of Environmental Biology, which funded the research along with NSF's Division of Earth Sciences.

"This capability will advance the field of paleoecology and greatly improve our understanding of how future climate change will reshape ecosystems."

The team focused its fieldwork on several sites in Patagonia, which have some of the best preserved fossils in the world.

For years, paleontologists have painstakingly collected fossils from these sites and worked to precisely determine their ages using radiometric dating. The new study builds on this growing body of knowledge.

In Patagonia and other places, scientists have some idea based on records of fossilized pollen and leaves what species of plants were alive at given periods in history.

For example, the team's previous work documented vegetation composition for this area.

But there hasn't been a way to precisely quantify vegetation openness, aside from general speculations of open or bare habitats, as opposed to closed or tree-covered habitats.

"These researchers have developed a new method for reconstructing paleo-vegetation structure in open versus dense forests using plant biosilica, likely to be widely found in the fossil record," says Chris Liu, program director in NSF's Division of Earth Sciences.

"Now we have a tool to look at a lot of important intervals in our history where we don't know what happened to the structure of vegetation," adds Dunn, such as the period just after the mass extinction that killed the dinosaurs.

"Vegetation structure links all aspects of modern ecosystems, from soil moisture to primary productivity to global climate," says paper co-author Caroline Stromberg, a curator of paleobotany at the Burke Museum.

"Using this method, we can finally quantify in detail how Earth's plant and animal communities have responded to climate change over millions of years, vital for forecasting how ecosystems will change under predicted future climate scenarios."

Plant cell patterns change with sun exposure

Work by other scientists has shown that the cells found in a plant's outermost layer, called the epidermis, change in size and shape depending on how much sun it's exposed to while its leaves develop.

For example, the cells of a leaf that grow in deeper shade will be larger and curvier than the cells of leaves that develop in less covered areas.

Dunn and collaborators found that these cell patterns, indicating growth in shade or sun, similarly show up in some plant fossils.

When a plant's leaves fall to the ground and decompose, tiny silica particles inside the plants, called phytoliths, remain as part of the soil layer.

The phytoliths were found to represent epidermal cell shapes and sizes, indicating whether the plant grew in a shady or open area.

The researchers decided to check their hypothesis by testing it in a modern setting: Costa Rica.

Dunn took soil samples from sites in Costa Rica that varied from covered rainforests to open savannas to woody shrublands.

She also took photos looking directly up at the tree canopy (or lack thereof) at each site, noting the total vegetation coverage.

Back in the lab, she extracted the phytoliths from each soil sample and measured them under the microscope.

When compared with tree coverage estimated from the corresponding photos, Dunn and co-authors found that the curves and sizes of the cells directly related to how shady their environment was.

"Leaf area index" and plant cell structures compared

The researchers characterized the amount of shade as "leaf area index," a standard way of measuring vegetation over a specific area.

Testing this relationship between leaf area index and plant cell structures in modern environments allowed the scientists to develop an equation that can be used to predict vegetation openness at any time in the past, provided there are preserved plant fossils.

"Leaf area index is a well-known variable for ecologists, climate scientists and modelers, but no one's ever been able to imagine how you could reconstruct tree coverage in the past--and now we can," says co-author Richard Madden of the University of Chicago.

"We should be able to reconstruct leaf area index by using all kinds of fossil plant preservation, not just phytoliths. Once that is demonstrated, then the places in the world where we can reconstruct this will increase."

When Dunn and co-authors applied their method to 40-million-year-old phytoliths from Patagonia, they found something surprising--vegetation was extremely open, similar to a shrubland today. The appearance of these very open habitats coincided with major changes in fauna.

The paleobiologists plan to test the relationship between vegetation coverage and plant cell structure in other regions around the world.

They also hope to find other types of plant fossils that hold the same information at the cellular level as do phytoliths.

Paper co-authors are Matthew Kohn of Boise State University and Alfredo Carlini of Universidad Nacional de La Plata in Argentina.

In addition to NSF, the research was funded by the Geological Society of America, the University of Washington Biology Department and the Burke Museum.

-NSF-
Media Contacts
Cheryl Dybas, NSF

SCIENTISTS LOOK TO SUNFLOWERS FOR ANSWERS

FROM:  NATIONAL SCIENCE FOUNDATION 

Ten things to know about the flowers of fall: Sunflowers

Scientists unfurl common flowers' genetic secrets

As fall fields turn bright with color, what might we learn from roadside rows of sunflowers--and the sunflower seeds widely used to feed birds in colder weather?

Scientists are finding that answers to biological and environmental questions large and small may be hidden in the petals of common sunflowers.

For example, how frequently and under what conditions does evolution take the same path? When independent populations evolve the same characteristics, are the underlying genetic changes similar or different?

To peer into the world of speciation--how one species branches into another--the National Science Foundation (NSF) spoke with George Gilchrist, a program director in the agency's Division of Environmental Biology and with Ken Whitney, a plant biologist at the University of New Mexico who studies populations of experimental sunflowers in Texas.

With funding from NSF, Whitney and botanist Loren Rieseberg of Indiana University Bloomington and the University of British Columbia are learning whether sunflowers are converging or diverging in their traits.

1) Why do scientists study sunflowers?

Whitney (KW): Sunflowers represent a "recent" success story. In the past three million years, this group has diverged (or branched into new species) in some 50 species in North America. Sunflowers live in a variety of habitats, from forests to deserts to salt marshes.

Sunflowers also contain examples of many important processes, including the evolution of both annual and perennial lifestyles, hybridization (mating between species) and the phenomena of polyploidy (the doubling of chromosome sets in a lineage). All this combines in an "evolutionary cauldron."

2) Where did sunflowers originate?

(KW): The genus Helianthus, true sunflowers, is native to North America. The common sunflower, H. annuus, and its seeds are one of only three crops that were domesticated north of Mexico. The second, sumpweed, was a favorite of Native Americans, but is no longer in use; the third, Jerusalem artichoke, is actually the root of another sunflower species, H. tuberosus.

3) What are the major commercial uses of sunflowers?

(KW): Oilseed sunflower varieties are used to produce oil used in cooking. A separate set of varieties, called confectionary varieties, has been developed to produce the large seeds we eat directly--such as those that are roasted and salted.

4) How do sunflowers link North America and Russia?

(KW): Although the crop sunflower originated in North America, it had to travel to Europe to achieve its current form. Much of the breeding for large seed size and high oil content was done in Russia in the 1800s, a legacy that is still with us in the sunflower variety called "Russian Mammoth." Many of us grow this plant in home gardens.

Sunflower varieties from Russia made it back to the U.S. in the late 1880s, but it was not until the 1930s and 1940s that crop sunflowers were grown on a large commercial scale in the United States.

5) What's the difference between wild sunflowers and those that are domesticated and grown as crops?

(KW): Both wild and crop sunflowers are the same species, H. annuus. Wild sunflowers have many flowering heads on each plant, and have small seeds. A major event in the domestication of the sunflower was the creation of a "monocephalic" plant with a single large flowering head and large seeds.

6) How much diversity is there in wild sunflowers?

(KW): The 50 or so species of wild sunflowers are both ecologically and genetically diverse. The U.S. Department of Agriculture maintains seed stocks of most wild sunflower species, in part because they contain genetic material that can be used to improve cultivated sunflower varieties. For example, a pest-resistant species might provide genes that could decrease pest damage in cultivated sunflowers.

7) What ecological factors drive sunflowers' diversity?

(KW): Sunflowers live in a wide range of habitats, and are widespread across the North American continent. That geographic range means that sunflowers have adapted to very different environmental conditions during the course of their radiation.

8) Are there medical treatments derived from sunflower products?

(KW): Sunflower products, especially the oil from the seeds, have long been used in folk medicine, but I'm not aware of any uses in modern medicine.

9) Do wild sunflowers hybridize? What role has hybridization played in speciation?

(KW): Sunflowers are notorious for hybridizing: mating across species boundaries and exchanging genetic material between species. Sometimes this genetic exchange leads to improved performance, for example in the Texas sunflower our team has been studying.

We have evidence that when wild H. annuus captured genes from another species, H. debilis, it was able to expand its range southward and become a new subspecies, H. annuus texanus. In other sunflowers, hybridization may lead to entirely new species. The sunflowers H. annuus and H. petiolaris have hybridized repeatedly and have produced three new sunflower species that live on the desert floor, on sand dunes, and in salt marshes.

Gilchrist (GG): This research has been critical to understanding how hybridization can lead to rapid speciation. While many hybrids are sterile, some genetic changes create hybrids with extra sets of chromosomes that are fully fertile, but reproductively isolated from their parents.

These new hybrid sunflowers often are uniquely adapted to new habitats that neither of the parent species occupies. Speciation by hybridization is very common in plants and may play a major role in plant diversification.

10) Do insects and pathogens attack sunflowers?

(KW): Sunflowers are indeed attacked by insects, especially grasshoppers, caterpillars, aphids and their relatives, as well as by fungal and bacterial pathogens.

A sunflower's life, scientists say, is no bed of roses.

-- Cheryl Dybas,

DOE SECRETARY VISITS LOS ALAMOS NATIONAL LABORATORY

FROM:  LOS ALAMOS NATIONAL LABORATORY 
DOE secretary stresses energy security during Los Alamos visit

Tours biology laboratory created in partnership with county, universities, LANL

LOS ALAMOS, N.M., Sept. 3, 2013—U.S. Secretary of Energy Ernest Moniz today during a visit to Los Alamos National Laboratory and the new biological laboratory built by the New Mexico Consortium (NMC) to explore alternative fuel sources from algae and other plants said that Los Alamos and all the DOE labs have a major role in addressing two key initiatives of the President.

“In view of the President's emphasis on nuclear security and climate change, the work at Los Alamos has never been more important," Secretary Moniz said.

Moniz also addressed Los Alamos employees and received briefings on the Laboratory’s nuclear weapons and intelligence work. It was the first visit by an Energy secretary to Los Alamos since 2009.

Moniz was accompanied by Rep. Ben Ray Luján and New Mexico Institute of Mining and Technology President Daniel Lopez.

The NMC is a non-profit formed by the three New Mexico research universities to engage universities and industry in scientific research in the nation's interest and to increase the role of Los Alamos National Laboratory (LANL) in science, education and economic development in the state.

The Biological Laboratory was built by the NMC in partnership with the County of Los Alamos, Los Alamos National Bank and Los Alamos National Laboratory. The County of Los Alamos played a critical role in the project, providing a $2.6 million toward construction of the building.

The NMC Biological Laboratory supports the LANL/NMC initiative in sustainable global energy and food security. This initiative pursues joint research on higher yielding biofuel production systems and more nutritious and higher yielding crops.

“Los Alamos National Laboratory has been forward thinking and innovative in pursuing new mechanisms to engage with universities and industry through the NMC. I am very excited about the future of this partnership. ” said NMC Executive Director Katharine Chartrand.