A new study overturns that hypothesis, presenting the first geological evidence that the ancestors of these and other C4 grasses emerged millions of years earlier than previously established.
The findings are published in the journal Geology.
C4 plants are more efficient than C3 plants at taking up atmospheric carbon dioxide and converting it into the starches and sugars vital to plant growth. (C3 and C4 refer to the number of carbon atoms in the first molecular product of photosynthesis.) Having evolved relatively recently, C4 plants make up 3 percent of all living species of flowering plants. But they account for about 25 percent of global plant productivity on land. They dominate grasslands in tropical, subtropical and warm temperate areas. They also are a vital food source and an important feedstock for the production of biofuels.
"C4 plants are very successful, they're economically very important, but we actually don't know when they originated in the geological history," said University of Illinois plant biology professor Feng Sheng Hu, who led the new analysis. "To me, it's one of the most profound geological and ecological questions as a paleoecologist I can tackle."
A previous study dated the oldest C4 plant remnant found, a tiny fragment called a phytolith, to about 19 million years ago. Other studies analyzed the ratios of carbon isotopes in bulk soil samples to determine the ratio of C3 to C4 plant remains at different soil horizons, which correspond to different geological time periods. (C3 and C4 plants differ in their proportions of two carbon isotopes, C-12 and C-13.) Those studies indicated that C4 grasses were present as early as the Early Micocene, about 18 million years ago.
Rather than analyzing plant matter in bulk sediment samples, David Nelson, a postdoctoral researcher in Hu's lab at the time of the study (now a professor at the University of Maryland), analyzed the carbon isotope ratios of individual grains of grass pollen, a technique he pioneered while working with Hu in the lab of biogeochemistry professor Ann Pearson at Harvard University.
Using a spooling-wire micro-combustion device to combust the grains, and an isotope mass spectrometer to determine the relative ratio of C-12 and C-13 in the sample, Nelson and Illinois graduate student Michael Urban analyzed hundreds of individual grains of grass pollen collected from study sites in Spain and France.
"Because we analyze carbon isotopes in a material unique to grasses (pollen) we were able to detect C4 grasses at lower abundances than previous studies," Nelson said.
This analysis found "unequivocal evidence for C4 grasses in southwestern Europe by the Early Oligocene," the authors wrote. This means these grasses were present 32 to 34 million years ago, well before studies indicate atmospheric carbon dioxide levels made their precipitous decline.
"The evidence refutes the idea that low (atmospheric) CO2 was an important driver and/or precondition for the development of C4 photosynthesis," the authors wrote.
"This study challenges that hypothesis and basically says that something else was responsible for the evolution of C4 plants, probably higher temperature or drier conditions," Hu said. With atmospheric carbon dioxide levels now on the increase, he said, "there are also implications about how C3 and C4 plants will fare in the future."
Researchers from Harvard University; the Universidad de Granada, Spain; and the Bureau de Recherche Géologiques et Minières, France, also contributed to the study.
The University of Illinois Research Board, the National Science Foundation, and the David and Lucille Packard Foundation Fellowships Program supported this study.
Editor's notes: To reach Feng Sheng Hu, call 217-244-2982; e-mail email@example.com.
The paper, "Isotopic Evidence of C4 Grasses in Southwestern Europe During the Early Oligocene-Middle Miocene," is available online and from the U. of I. News Bureau.
Diana Yates | EurekAlert!
A sudden drop in outdoor temperature increases the risk of respiratory infections
11.01.2017 | University of Gothenburg
Urbanization to convert 300,000 km2 of prime croplands
27.12.2016 | Mercator Research Institute on Global Commons and Climate Change (MCC) gGmbH
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).
Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...
Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.
The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...
UMD, NOAA collaboration demonstrates suitability of in-orbit datasets for weather satellite calibration
"Traffic and weather, together on the hour!" blasts your local radio station, while your smartphone knows the weather halfway across the world. A network of...
Fiber-reinforced plastics (FRP) are frequently used in the aeronautic and automobile industry. However, the repair of workpieces made of these composite materials is often less profitable than exchanging the part. In order to increase the lifetime of FRP parts and to make them more eco-efficient, the Laser Zentrum Hannover e.V. (LZH) and the Apodius GmbH want to combine a new measuring device for fiber layer orientation with an innovative laser-based repair process.
Defects in FRP pieces may be production or operation-related. Whether or not repair is cost-effective depends on the geometry of the defective area, the tools...
10.01.2017 | Event News
09.01.2017 | Event News
05.01.2017 | Event News
16.01.2017 | Power and Electrical Engineering
16.01.2017 | Information Technology
16.01.2017 | Power and Electrical Engineering