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‘Green Revolution’ changes breathing of the biosphere: Stronger seasonal oscillations in carbon dioxide linked to intensive agriculture

The intense farming practices of the “Green Revolution” are powerful enough to alter Earth’s atmosphere at an ever-increasing rate, boosting the seasonal amplitude in atmospheric carbon dioxide to about 15 percent over the past five decades.

That’s the key finding of a new atmospheric model developed by University of Maryland researchers, which estimates that on average, the amplitude of the seasonal oscillation of carbon dioxide in the atmosphere is increasing at a rate of 0.3 percent every year. A study based on the results of the model, called VEGAS, was published Nov. 20, 2014 in the journal Nature.

“What we are seeing is the effect of the Green Revolution on Earth’s metabolism,” said UMD Atmospheric and Ocean Science Professor Ning Zeng, the lead developer of VEGAS, a terrestrial carbon cycle model that, for the first time, factors in changes in 20th and 21st century farming practices. “Changes in the way we manage the land can literally alter the breathing of the biosphere.”

Scientists have known since the 1950s that carbon dioxide levels in the atmosphere hit an annual low during late summer and early fall in the Northern Hemisphere, which has a greater continental landmass than the Southern Hemisphere, and therefore has more plant life. The atmosphere’s carbon dioxide level falls in spring and summer as all the hemisphere’s plants reach their maximum growth, taking in carbon dioxide and releasing oxygen. In the autumn, when the hemisphere’s plants are decomposing and releasing stored carbon, the atmosphere’s carbon dioxide levels rapidly increase.

In a set of historic observations taken continuously since 1958 at Hawaii’s Mauna Loa Observatory, and later in other places including Barrow, Alaska, researchers have tracked these seasonal peaks and valleys, which clearly show an increase in the atmosphere’s overall level of carbon dioxide, Earth’s main greenhouse gas. Between 1961 and 2010, the seasonal variation has also become more extreme. Carbon dioxide levels are currently about 6 parts per million higher in the Northern Hemisphere’s winter than in summer.

While the forces driving the overall increase in carbon dioxide are well understood, the reasons behind the steepening of the seasonal carbon dioxide cycle are harder to pin down. Because plants breathe in carbon dioxide, higher atmospheric levels of the gas can stimulate plant growth, and this so-called “carbon dioxide fertilization effect” probably plays a role. Climate scientists also point to the warming in the Northern Hemisphere high latitudes that makes plants grow better in cold regions as an important factor. But even taken together, those factors cannot fully account for the trend and spatial patterns toward increasing seasonal change, said Zeng.

Zeng points out that between 1961 and 2010, the amount of land planted with major crops grew by 20 percent, but crop production tripled. The combination of factors known as the Green Revolution–improved irrigation, increased use of manufactured fertilizer, and higher-yield strains of corn, wheat, rice and other crops–must have led not only to increased crop productivity, but also to increases in plants’ seasonal growth and decay and the amount of carbon dioxide they release to the atmosphere, he reasoned.

UMD graduate student Fang Zhao and other collaborators worked with Zeng, who developed the first of several versions of the VEGAS model in 2000, to add information on worldwide crop production. The researchers combined country-by-country statistics collected yearly by the United Nations Food and Agricultural Organization (FAO) with climate data and observations of atmospheric carbon dioxide levels from several sites. To ensure that their results did not overstate the Green Revolution’s effect, the researchers ran their model using an estimate of worldwide crop production slightly lower than the FAO statistics.

Once the Green Revolution was factored in, VEGAS’ results generally tracked the actual carbon dioxide peaks and valleys recorded at Mauna Loa. Between 1975 and 1985, carbon dioxide levels rose faster at Mauna Loa than they did in the model, but this could be due to regional weather patterns, Zeng said.

Other atmospheric models factor in changes in land use, from natural vegetation to cropland, Zeng said, but the VEGAS results described in Nature are the first to track the effect of changes in the intensity of farming methods. There are still many unknowns. For example, the Green Revolution has not affected all parts of the world equally, and there isn’t enough detailed information about changing farming practices over the past 50 years to build those detailed variations into the model.

“We dealt with the unknowns by keeping it simple,” said Zeng. “My education was mostly in physics, and physicists are brave about making the simplifying assumptions you have to make to reach a general understanding of some important force. Our goal was simply to represent the intensification of agriculture in a model of the carbon cycle, and we have accomplished that.”

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The above story is based on materials provided by University of Maryland. The original article was written by Heather Dewar. Note: Materials may be edited for content and length.

Agriculture and Food News — ScienceDaily

Discovery provides insights on how plants respond to elevated carbon dioxide levels

Biologists at UC San Diego have solved a long-standing mystery concerning the way plants reduce the numbers of their breathing pores in response to rising carbon dioxide levels in the atmosphere.

In a paper published in this week’s early online edition of Nature, they report the discovery of a new genetic pathway in plants, made up of four genes from three different gene families that control the density of breathing pores—or “stomata”—in plant leaves in response to elevated CO2 levels.

Their discovery should help biologists better understand how the steadily increasing levels of CO2 in our atmosphere (which last spring, for the first time in recorded history, remained above 400 parts per million) are affecting the ability of plants and economically important crops to deal with heat stress and drought. It could also provide agricultural scientists with new tools to engineer plants and crops that can deal with droughts and high temperatures like those now affecting the Southwestern United States.

“For each carbon dioxide molecule that is incorporated into plants through photosynthesis, plants lose about 200 hundred molecules of water through their stomata,” explains Julian Schroeder, a professor of biology who headed the research effort. “Because elevated CO2 reduces the density of stomatal pores in leaves, this is, at first sight beneficial for plants as they would lose less water. However, the reduction in the numbers of stomatal pores decreases the ability of plants to cool their leaves during a heat wave via water evaporation. Less evaporation adds to heat stress in plants, which ultimately affects crop yield.”

Schroeder is also co-director of a new research entity at UC San Diego called “Food and Fuel for the 21st Century,” which is designed to apply basic research on plants to sustainable food and biofuel production.

“Our research is aimed at understanding the fundamental mechanisms and genes by which CO2 represses stomatal pore development,” says Schroeder. Working in a tiny mustard plant called Arabidopsis, which is used as a genetic model and shares many of the same genes as other plants and crops, he and his team of biologists discovered that the proteins encoded by the four genes they discovered repress the development of stomata at elevated CO2 levels.

Using a combination of systems biology and bioinformatic techniques, the scientists cleverly isolated proteins, which, when mutated, abolished the plant’s ability to respond to CO2 stress. Cawas Engineer, a postdoctoral scientist in Schroeder’s lab and the first author of the study, found that when plants sense atmospheric CO2 levels rising, they increase their expression of a key peptide hormone called Epidermal Patterning Factor-2, EPF2.

“The EPF2 peptide acts like a morphogen which alters stem cell character in the epidermis of growing leaves and blocks the formation of stomata at elevated CO2,” explains Engineer.

Because other proteins known as proteases are needed to activate the EPF2 peptide, the scientists also used a “proteomics” approach to identify a new protein that they called CRSP (CO2 Response Secreted Protease) which, they determined, is crucial for activating the EPF2 peptide.

“We identified CRSP, a secreted protein, which is responsive to atmospheric CO2 levels,” says Engineer. “CRSP plays a pivotal role in allowing the plant to produce the right amount of stomata in response to the concentration of CO2 in the atmosphere. You can imagine that such a ‘sensing and response’ mechanism involving CRSP and EPF2 could be used to engineer crop varieties which are better able to perform in the current and future high CO2 global climate where fresh water availability for agriculture is dwindling.”

The discoveries of these proteins and genes have the potential to address a wide range of critical agricultural problems in the future, including the limited availability of water for crops, the need to increase water use efficiency in lawns as well as crops and concerns among farmers about the impact heat stress will have in their crops as global temperatures and CO2 levels continue to rise.

“At a time where the pressing issues of climate change and inherent agronomic consequences which are mediated by the continuing atmospheric CO2 rise are palpable, these advances could become of interest to crop biologists and climate change modelers,” says Engineer.

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The above story is based on materials provided by University of California – San Diego. The original article was written by Kim McDonald. Note: Materials may be edited for content and length.

Agriculture and Food News — ScienceDaily

Food quality will suffer with rising carbon dioxide, field study shows

For the first time, a field test has demonstrated that elevated levels of carbon dioxide inhibit plants’ assimilation of nitrate into proteins, indicating that the nutritional quality of food crops is at risk as climate change intensifies.

Findings from this wheat field-test study, led by a UC Davis plant scientist, will be reported online April 6 in the journal Nature Climate Change.

“Food quality is declining under the rising levels of atmospheric carbon dioxide that we are experiencing,” said lead author Arnold Bloom, a professor in the Department of Plant Sciences.

“Several explanations for this decline have been put forward, but this is the first study to demonstrate that elevated carbon dioxide inhibits the conversion of nitrate into protein in a field-grown crop,” he said.

The assimilation, or processing, of nitrogen plays a key role in the plant’s growth and productivity. In food crops, it is especially important because plants use nitrogen to produce the proteins that are vital for human nutrition. Wheat, in particular, provides nearly one-fourth of all protein in the global human diet.

Many previous laboratory studies had demonstrated that elevated levels of atmospheric carbon dioxide inhibited nitrate assimilation in the leaves of grain and non-legume plants; however there had been no verification of this relationship in field-grown plants.

Wheat field study

To observe the response of wheat to different levels of atmospheric carbon dioxide, the researchers examined samples of wheat that had been grown in 1996 and 1997 in the Maricopa Agricultural Center near Phoenix, Ariz.

At that time, carbon dioxide-enriched air was released in the fields, creating an elevated level of atmospheric carbon at the test plots, similar to what is now expected to be present in the next few decades. Control plantings of wheat were also grown in the ambient, untreated level of carbon dioxide.

Leaf material harvested from the various wheat tests plots was immediately placed on ice, and then was oven dried and stored in vacuum-sealed containers to minimize changes over time in various nitrogen compounds.

A fast-forward through more than a decade found Bloom and the current research team able to conduct chemical analyses that were not available at the time the experimental wheat plants were harvested.

In the recent study, the researchers documented that three different measures of nitrate assimilation affirmed that the elevated level of atmospheric carbon dioxide had inhibited nitrate assimilation into protein in the field-grown wheat.

“These field results are consistent with findings from previous laboratory studies, which showed that there are several physiological mechanisms responsible for carbon dioxide’s inhibition of nitrate assimilation in leaves,” Bloom said.

3 percent protein decline expected

Bloom noted that other studies also have shown that protein concentrations in the grain of wheat, rice and barley — as well as in potato tubers — decline, on average, by approximately 8 percent under elevated levels of atmospheric carbon dioxide.

“When this decline is factored into the respective portion of dietary protein that humans derive from these various crops, it becomes clear that the overall amount of protein available for human consumption may drop by about 3 percent as atmospheric carbon dioxide reaches the levels anticipated to occur during the next few decades,” Bloom said.

While heavy nitrogen fertilization could partially compensate for this decline in food quality, it would also have negative consequences including higher costs, more nitrate leaching into groundwater and increased emissions of the greenhouse gas nitrous oxide, he said.

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The above story is based on materials provided by University of California – Davis. Note: Materials may be edited for content and length.

Agriculture and Food News — ScienceDaily