Phytoplankton species deviates from norm: No CO2 absorbed in photosynthesis

A widespread species of ocean-dwelling microorganisms has been found to employ a never-before-seen alternative method of photosynthesis.

The discovery has implications not only for scientists' basic understanding of photosynthesis—arguably the most important biological process on Earth—but also for the amount of carbon dioxide that phytoplankton pull from the atmosphere.

Until now, it was thought that all the photosynthetic algae and bacteria living in the ocean drew carbon dioxide out of the air and used it to build sugars and other carbon-rich molecules to use as fuel. But two new studies by researchers at Stanford and the Carnegie Institution show that Synechococcus, a type of cyanobacteria (formerly called blue-green algae) that dominates much of the world's oceans, has evolved a mechanism that short-circuits photosynthetic carbon-dioxide fixation while still producing energy. The alternate approach is found in regions of the ocean where some of the ingredients necessary for traditional photosynthesis are in short supply.

"The amount of carbon dioxide being drawn down by the phytoplankton in nutrient-poor oceans might turn out to be significantly lower than we thought," said Shaun Bailey, a postdoctoral researcher working in the Carnegie Institution's Department of Plant Biology with Arthur Grossman, a staff scientist at the institution and a professor, by courtesy, in Stanford's Biology Department.

Bailey is the lead author of the paper describing part of the work in Biochimica et Biophysica Acta 1777 (2008). Kate Mackey, a graduate student in civil and environmental engineering at Stanford, is lead author of a second paper describing the work, currently in press at Limnology and Oceanography.

Until now, researchers have estimated marine photosynthetic activity by analyzing satellite images of the world's oceans to determine how much chlorophyll was in the water. Since chlorophyll is needed for photosynthesis, it was thought that measuring its concentration would be a straightforward way of estimating the amount of photosynthesis that would occur and therefore how much carbon dioxide would be consumed, or "fixed," by the phytoplankton. But the new work suggests that the relationship between the amount of chlorophyll in the water and the amount of carbon dioxide fixation by phytoplankton is not consistent throughout the world's oceans.

"There is a new twist on photosynthesis here, and that has to be accounted for when it comes to CO2 modeling," Bailey said, adding that, in some cases, the models may overestimate the amount of carbon fixation that occurs in nutrient-poor waters.

It is not yet clear what the finding might mean to studies of long-term global warming, he said, but it will have to be incorporated into any models that include carbon fixing by phytoplankton as a factor.

Synechococcus caught the interest of Grossman and his team because it thrives in vast areas of the ocean that are relatively deficient in iron, an element that is critical for certain reactions in the normal process of photosynthesis. How Synechococcus could maintain its abundance in the face of that deficiency was a puzzle.

"It seems that Synechococcus in the oligotrophic [nutrient-poor] oceans has solved the iron problem, at least in part by short-circuiting the standard photosynthetic process," Grossman said. "Much of the time this organism bypasses stages in photosynthesis that require the most iron. As it turns out, these are also the stages in which CO2 is taken from the atmosphere."

"We realized very quickly that there was something different about the Synechococcus that we were studying," said Bailey, the lead postdoctoral fellow working on the project. "The uptake of CO2 and the photosynthetic activities didn't match, so we knew that something other than CO2 was being consumed by photosynthesis, and it turned out to be oxygen." The researchers have tentatively identified the enzyme involved in this process to be plastoquinol terminal oxidase, or PTOX.

Bailey worked with Synechococcus in the laboratory, but recently this newly discovered phenomenon was shown to occur in nature by Mackey, who made direct measurements of photosynthesis in field samples from the Atlantic and Pacific oceans.

"The low-nutrient, low-iron environments account for about half of the area of the world's oceans, so they represent a large portion of the Earth's surface available for photosynthesis," Mackey said. "Our findings show that this novel cycle occurs in two major ocean basins and suggest that a substantial amount of energy from sunlight gets re-routed away from carbon fixation during photosynthesis. This may mean that less CO2 is being removed from the atmosphere by the open ocean photosynthetic organisms than was previously believed."

"This discovery represents a paradigm shift in our view of photosynthesis by organisms in the vast, nutrient-starved areas of the open ocean," said Joe Berry of the Carnegie Institution's Department of Global Ecology. "We had assumed that like higher plants, the goal was to make carbohydrates from CO2 and store them for later use as a source of energy for any number of cellular functions or growth. We now know that some organisms short-circuit this complicated process, using light in a minimalist way to power cellular processes directly with a far simpler and cheaper—in terms of scarce nutrients such as iron—photosynthetic apparatus. We don't know the full significance of this finding yet, but it is certain to change the way we interpret optical measurements of photosynthetic pigments in the ocean and the way we model ocean productivity."

Wolf Frommer, director of the Carnegie Institution's Department of Plant Biology, agreed on the discovery's ground-breaking importance. "If we thought we have understood photosynthesis, this study proves that there is much to be learned about these basic physiological processes," he said.

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Black carbon pollution growing

Black carbon, a form of particulate air pollution most often produced from biomass burning, cooking with solid fuels and diesel exhaust, has a warming effect in the atmosphere three to four times greater than prevailing estimates, according to scientists in an upcoming review article in the journal Nature Geoscience.

Scripps Institution of Oceanography at UC San Diego atmospheric scientist V. Ramanathan and University of Iowa chemical engineer Greg Carmichael, said that soot and other forms of black carbon could have as much as 60 percent of the current global warming effect of carbon dioxide, more than that of any greenhouse gas besides CO2. The researchers also noted, however, that mitigation would have immediate societal benefits in addition to the long term effect of reducing greenhouse gas emissions.

The article, “Global and regional climate changes due to black carbon,” will be posted in the online version of Nature Geoscience on March 23.

“Observationally based studies such as ours are converging on the same large magnitude of black carbon heating as modeling studies from Stanford, Caltech and NASA,” said Ramanathan. “We now have to examine if black carbon is also having a large role in the retreat of arctic sea ice and Himalayan glaciers as suggested by recent studies.”

In the paper, Ramanathan and Carmichael integrated observed data from satellites, aircraft and surface instruments about the warming effect of black carbon and found that its forcing, or warming effect in the atmosphere, is about 0.9 watts per meter squared. That compares to estimates of between 0.2 watts per meter squared and 0.4 watts per meter squared that were agreed upon as a consensus estimate in a report released last year by the Intergovernmental Panel on Climate Change (IPCC), a U.N.-sponsored agency that periodically synthesizes the body of climate change research.

Ramanathan and Carmichael said the conservative estimates are based on widely used computer model simulations that do not take into account the amplification of black carbon’s warming effect when mixed with other aerosols such as sulfates. The models also do not adequately represent the full range of altitudes at which the warming effect occurs. The most recent observations, in contrast, have found significant black carbon warming effects at altitudes in the range of 2 kilometers (6,500 feet), levels at which black carbon particles absorb not only sunlight but also solar energy reflected by clouds at lower altitudes.

Between 25 and 35 percent of black carbon in the global atmosphere comes from China and India, emitted from the burning of wood and cow dung in household cooking and through the use of coal to heat homes. Countries in Europe and elsewhere that rely heavily on diesel fuel for transportation also contribute large amounts.

“Per capita emissions of black carbon from the United States and some European countries are still comparable to those from south Asia and east Asia,” Ramanathan said.

In south Asia, pollution often forms a prevalent brownish haze that has been termed the “atmospheric brown cloud.” Ramanathan’s previous research has indicated that the warming effects of this smog appear to be accelerating the melt of Himalayan glaciers that provide billions of people throughout Asia with drinking water. In addition, the inhalation of smoke during indoor cooking has been linked to the deaths of an estimated 400,000 women and children in south and east Asia.

Elimination of black carbon, a contributor to global warming and a public health hazard, offers a nearly instant return on investment, the researchers said. Black carbon particles only remain airborne for weeks at most compared to carbon dioxide, which remains in the atmosphere for more than a century. In addition, technology that could substantially reduce black carbon emissions already exists in the form of commercially available products.

Ramanathan said that an observation program for which he is currently seeking corporate sponsorship could dramatically illustrate the benefits. Known as Project Surya, the proposed venture would provide some 20,000 rural Indian households with smoke-free cookers and equipped to transmit data. At the same time, a team of researchers led by Ramanathan would observe air pollution levels in the region to measure the effect of the cookers.

Carmichael said he hopes that the paper’s presentation of the immediacy of the benefits will make it easier to generate political and regulatory momentum toward reduction of black carbon emissions.

“It offers a chance to get better traction for implementing strategies for reducing black carbon,” he said.

The National Science Foundation, the National Oceanic and Atmospheric Administration and the National Aeronautics and Space Administration funded the review.

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New UC analysis shows alarming increase in expected growth of China's CO2 emissions

The growth in China's carbon dioxide (CO2) emissions is far outpacing previous estimates, making the goal of stabilizing atmospheric greenhouse gases much more difficult, according to a new analysis by economists at the University of California, Berkeley, and UC San Diego.

Previous estimates, including those used by the Intergovernmental Panel on Climate Change, say the region that includes China will see a 2.5 to 5 percent annual increase in CO2 emissions, the largest contributor to atmospheric greenhouse gases, between 2004 and 2010. The new UC analysis puts that annual growth rate for China to at least 11 percent for the same time period.

The study is scheduled for print publication in the May issue of the Journal of Environmental Economics and Management, but is now online.

The researchers' most conservative forecast predicts that by 2010, there will be an increase of 600 million metric tons of carbon emissions in China over the country's levels in 2000. This growth from China alone would dramatically overshadow the 116 million metric tons of carbon emissions reductions pledged by all the developed countries in the Kyoto Protocol. (The protocol was never ratified in the United States, which was the largest single emitter of carbon dioxide until 2006, when China took over that distinction, according to numerous reports.)

Put another way, the projected annual increase in China alone over the next several years is greater than the current emissions produced by either Great Britain or Germany.

Based upon these findings, the authors say current global warming forecasts are "overly optimistic," and that action is urgently needed to curb greenhouse gas production in China and other rapidly industrializing countries.

The authors of the study, Maximillian Auffhammer, UC Berkeley assistant professor of agricultural and resource economics, and Richard Carson, UC San Diego professor of economics, based their findings upon pollution data from China's 30 provincial entities.

Auffhammer said this paper should serve as an alarm challenging the widely held belief that actions taken by the wealthy, industrialized nations alone represent a viable strategy towards the goal of stabilizing atmospheric concentrations of carbon dioxide.

"Making China and other developing countries an integral part of any future climate agreement is now even more important," said Auffhammer. "It had been expected that the efficiency of China's power generation would continue to improve as per capita income increased, slowing down the rate of CO2 emissions growth. What we're finding instead is that the emissions growth rate is surpassing our worst expectations, and that means the goal of stabilizing atmospheric CO2 is going to be much, much harder to achieve."

Researchers traditionally calculate the CO2 emissions for a region or country from data on fossil fuel consumption. Existing models then use those emission figures and factor in such variables as population size, a society's affluence and technology developments to forecast the growth of greenhouse gas emissions.

In explaining the startling differences in results from previous estimates for China's carbon emissions growth, the UC researchers point out that they used province-level figures in their analysis to obtain a more detailed picture of the country's CO2 emissions up to 2004.

"Everybody had been treating China as single country, but each of the country's provinces is larger than many European countries, both in geographic size and population," said Carson. "In addition, there is a wide range in economic development and wealth from one province to the next, as well as major differences in population growth, all of which has an effect on energy consumption that cannot be easily addressed in models based upon aggregate national data."

Since data on fossil fuel consumption is not reported at the province level in China, the researchers used waste gas emissions, available from China's state environmental protection administration reports, as a proxy for CO2 emissions in this paper.

Moreover, the researchers said, the majority of other studies forecasting China's CO2 emissions relied upon information from nearly a decade ago. During the 1990s, per capita income was growing faster than the use of energy in China, which typically relates to slower growth in carbon emissions.

"A notable shift occurred in China around the year 2000, around the time when hope for an agreement with the U.S. on the Kyoto Protocol began to diminish along with external pressure for China to reduce its emissions," said Carson. "Energy use started to grow faster than income, and much of the energy that was used wasn't efficient."

The authors also pointed out that after 2000, China's central government began shifting the responsibility for building new power plants to provincial officials who had less incentive and fewer resources to build cleaner, more efficient plants, which save money in the long run but are more expensive to construct.

"Government officials turned away from energy efficiency as an objective to expanding power generation as quickly as they can, and as cheaply as they can," said Carson. "Wealthier coastal provinces tended to build clean-burning power plants based upon the very best technology available, but many of the poorer interior provinces replicated inefficient 1950s Soviet technology."

"The problem is that power plants, once built, are meant to last for 40 to 75 years," said Carson. "These provincial officials have locked themselves into a long-run emissions trajectory that is much higher than people had anticipated. Our forecast incorporates the fact that much of China is now stuck with power plants that are dirty and inefficient."

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Special Coating Greatly Improves Solar Cell Performance

The energy from sunlight falling on only 9 percent of California’s Mojave Desert could power all of the United States’ electricity needs if the energy could be efficiently harvested, according to some estimates. Unfortunately, current-generation solar cell technologies are too expensive and inefficient for wide-scale commercial applications.

A team of Northwestern University researchers has developed a new anode coating strategy that significantly enhances the efficiency of solar energy power conversion. A paper about the work, which focuses on “engineering” organic material-electrode interfaces in bulk-heterojunction organic solar cells, is published online this week in the Proceedings of the National Academy of Sciences (PNAS).

This breakthrough in solar energy conversion promises to bring researchers and developers worldwide closer to the goal of producing cheaper, more manufacturable and more easily implemented solar cells. Such technology would greatly reduce our dependence on burning fossil fuels for electricity production as well as reduce the combustion product: carbon dioxide, a global warming greenhouse gas.

Tobin J. Marks, the Vladimir N. Ipatieff Research Professor in Chemistry in the Weinberg College of Arts and Sciences and professor of materials science and engineering, and Robert Chang, professor of materials science and engineering in the McCormick School of Engineering and Applied Science, led the research team. Other Northwestern team members were researcher Bruce Buchholz and graduate students Michael D. Irwin and Alexander W. Hains.

Of the new solar energy conversion technologies on the horizon, solar cells fabricated from plastic-like organic materials are attractive because they could be printed cheaply and quickly by a process similar to printing a newspaper (roll-to-roll processing).

To date, the most successful type of plastic photovoltaic cell is called a “bulk-heterojunction cell.” This cell utilizes a layer consisting of a mixture of a semiconducting polymer (an electron donor) and a fullerene (an electron acceptor) sandwiched between two electrodes -- one a transparent electrically conducting electrode (the anode, which is usually a tin-doped indium oxide) and a metal (the cathode), such as aluminum.

When light enters through the transparent conducting electrode and strikes the light-absorbing polymer layer, electricity flows due to formation of pairs of electrons and holes that separate and move to the cathode and anode, respectively. These moving charges are the electrical current (photocurrent) generated by the cell and are collected by the two electrodes, assuming that each type of charge can readily traverse the interface between the polymer-fullerene active layer and the correct electrode to carry away the charge -- a significant challenge.

The Northwestern researchers employed a laser deposition technique that coats the anode with a very thin (5 to 10 nanometers thick) and smooth layer of nickel oxide. This material is an excellent conductor for extracting holes from the irradiated cell but, equally important, is an efficient “blocker” which prevents misdirected electrons from straying to the “wrong” electrode (the anode), which would compromise the cell energy conversion efficiency.

In contrast to earlier approaches for anode coating, the Northwestern nickel oxide coating is cheap, electrically homogeneous and non-corrosive. In the case of model bulk-heterojunction cells, the Northwestern team has increased the cell voltage by approximately 40 percent and the power conversion efficiency from approximately 3 to 4 percent to 5.2 to 5.6 percent.

The researchers currently are working on further tuning the anode coating technique for increased hole extraction and electron blocking efficiency and moving to production-scaling experiments on flexible substrates.

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Destroying native ecosystems for biofuel crops will worsen global warming

Turning native ecosystems into "farms" for biofuel crops causes major carbon emissions that worsen the global warming that biofuels are meant to mitigate, according to a new study by the University of Minnesota and the Nature Conservancy.

The work will be published in Science later this month and will be posted online Thursday, Feb. 7.

The carbon lost by converting rainforests, peatlands, savannas, or grasslands outweighs the carbon savings from biofuels. Such conversions for corn or sugarcane (ethanol), or palms or soybeans (biodiesel) release 17 to 420 times more carbon than the annual savings from replacing fossil fuels, the researchers said. The carbon, which is stored in the original plants and soil, is released as carbon dioxide, a process that may take decades. This "carbon debt" must be paid before the biofuels produced on the land can begin to lower greenhouse gas levels and ameliorate global warming.

The conversion of peatlands for palm oil plantations in Indonesia ran up the greatest carbon debt, one that would require 423 years to pay off. The next worst case was the production of soybeans in the Amazon, which would not "pay for itself" in renewable soy biodiesel for 319 years.

"We don't have proper incentives in place because landowners are rewarded for producing palm oil and other products but not rewarded for carbon management," said University of Minnesota Applied Economics professor Stephen Polasky, an author of the study. "This creates incentives for excessive land clearing and can result in large increases in carbon emissions.

"This research examines the conversion of land for biofuels and asks the question 'Is it worth it?'," said lead author Joe Fargione, a scientist for The Nature Conservancy. "And surprisingly, the answer is no."

Fargione began the work as a University of Minnesota postdoctoral researcher with Polasky, Regents Professor of Ecology David Tilman; he completed it after joining the Nature Conservancy. They, along with university researchers Jason Hill and Peter Hawthorne, also contributed to the work.

"If you're trying to mitigate global warming, it simply does not make sense to convert land for biofuels production," said Fargione. "All the biofuels we use now cause habitat destruction, either directly or indirectly. Global agriculture is already producing food for six billion people. Producing food-based biofuel, too, will require that still more land be converted to agriculture."

These findings coincide with observations that increased demand for ethanol corn crops in the United States is likely contributing to conversion of the Brazilian Amazon and Cerrado (tropical savanna). American farmers traditionally rotated corn crops with soybeans, but now they are planting corn every year to meet the ethanol demand and Brazilian farmers are planting more of the world's soybeans. And they're deforesting the Amazon to do it.

The researchers also found significant carbon debt in the conversion of grasslands in the United States and rainforests in Indonesia.

Researchers did note that some biofuels do not contribute to global warming because they do not require the conversion of native habitat. These include waste from agriculture and forest lands and native grasses and woody biomass grown on marginal lands unsuitable for crop production. The researchers urge that all fuels be fully evaluated for their impacts on global warming, including impacts on habitat conversion.

"Biofuels made on perennial crops grown on degraded land that is no longer useful for growing food crops may actually help us fight global warming," said Hill. "One example is ethanol made from diverse mixtures of native prairie plants. Minnesota is well poised in this respect."

"Creating some sort of incentive for carbon sequestration, or penalty for carbon emissions, from land use is vital if we are serious about addressing this problem," Polasky said.

"We will need to implement many approaches simultaneously to solve climate change. There is no silver bullet, but there are many silver BBs," said Fargione. "Some biofuels may be one silver BB, but only if produced without requiring additional land to be converted from native habitats to agriculture."

The work was supported by the University of Minesota's Initiative for Renewable Energy and the Environment and the National Science Foundation.

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