climate change and global warming

Climate change and Global Warming

In the past 60 years, the amount of carbon dioxide emitted, mainly through expanding use of fossil fuels for energy, has risen dramatically and is thought to contribute to global climate change. Unless we make major alterations in the way we produce and use energy, predictions for the next century suggest a continued increase in emissions as well as rising concentrations of carbon dioxide in the atmosphere. In addition to controlling fossil fuel emissions, other methods must be explored for stabilizing or decreasing carbon dioxide and other greenhouse gases.

One of the many poorly understood aspects of the global warming phenomenon is the role that specific microorganisms play in the natural carbon cycle on earth. As part of its Carbon Management Science Program, DOE hopes to stabilize or decrease atmospheric carbon dioxide concentrations by identifying ways to manage carbon levels in the terrestrial biosphere. One avenue of exploration is to sequence the genomes of microbes that use carbon dioxide as their sole carbon source. These organisms include Nitrosomonas europaea (pictured), Prochlorococcus marinus, Rhodopseudomonas palustris, Nostoc punctiforme, and a marine Synechococcus.

[Electron photomicrograph of Nitrosomonas, copyright Stan Watson

Study helps clarify role of soil microbes in global warming

Athens, Ga. - Current models of global climate change predict warmer temperatures will increase the rate that bacteria and other microbes decompose soil organic matter, a scenario that pumps even more heat-trapping carbon into the atmosphere. But a new study led by a University of Georgia researcher shows that while the rate of decomposition increases for a brief period in response to warmer temperatures, elevated levels of decomposition don't persist.

"There is about two and a half times more carbon in the soil than there is in the atmosphere, and the concern right now is that a lot of that carbon is going to end up in the atmosphere," said lead author Mark Bradford, assistant professor in the UGA Odum School of Ecology. "What our finding suggests is that a positive feedback between warming and a loss of soil carbon to the atmosphere is likely to occur but will be less than currently predicted."

Bradford, whose results appear in the early online edition of the journal Ecology Letters, said the finding helps resolve a long-standing debate about how unseen soil microbes respond to and influence global climate change. Other scientists have noted that the respiration of soil microbes returns to normal after a number of years under heated conditions, but offered competing explanations. Some argued that the microbes consumed so much of the available food under heated conditions that future levels of decomposition were reduced because of food scarcity. Others argued that soil microbes adapted to the changed environment and reduced their respiration accordingly.

Bradford and his team, which included researchers from the University of New Hampshire, the Marine Biological Laboratory at Woods Hole, Duke University and Colorado State University, found evidence to support both hypotheses and revealed a third, previously unaccounted for explanation: The abundance of soil microbes decreased under warm conditions.

"It is often said that in a handful of dirt, there are somewhere around 10,000 species and millions of individual bacteria and fungi," said study co-author Matthew Wallenstein, a research scientist at Colorado State University. "Our findings add to the understanding of how complex these systems are and the role they play in feedbacks associated with climate change."

The researchers studied soil microbes at Harvard Forest in Massachusetts, the site of a soil warming experiment that began in 1991. Scientists took soil samples from two plots, one in which buried cables heat the soil to five degrees Celsius above the ambient soil temperature (a condition that is expected to occur around 2100) and a control condition in which cables are buried but not producing heat.

In the first set of experiments, the scientists compared microbial respiration in the two groups and found lower rates of decomposition in the heated plots. This finding supported the idea that respiration decreases after a few years of warming, but didn't explain whether the cause was substrate depletion in the warmer soils or adaptation by the microbes.

In the next set of experiments, they added the simple sugar sucrose to both sets of soils to alleviate any food limitation for the microbes. They found that microbes from both conditions increased their respiration, but that the increase was greater in the unheated control soils than in the heated soils. "That finding told us that substrate depletion played a role," Bradford said, "but it also told us that there were other factors involved."

The researchers then measured microbial biomass and found that there were fewer microbes in the heated soils. To test whether thermal adaptation occurred, they measured respiration while keeping temperature constant. They found that respiration rates were indeed lower in the heated versus the control soils, even when adjusting for microbial biomass.

Wallenstein pointed out that the study is among the first to demonstrate that microbes, like many plants and animals, can adapt relatively quickly to changes in climate. "This research presents a new challenge to scientists trying to predict effects of climate change on forest ecosystems because it shows that these soil microbial communities are very dynamic," Wallenstein said. "We cannot simply extrapolate from the short-term responses of soil microbes to climate change, since they may adapt over the longer-term."

Bradford notes that there is still much to be learned about how soil microbes respond to global warming. His team is currently working to understand whether the reduced microbial respiration in heated soils is caused by the adaptation of individual microbes, by shifts in species composition or a combination of the two factors. He warns against minimizing the role of soil microbes in global warming, even though his findings suggest that current models overstate their contribution.

"Although our results suggest that the impact of soil microbes on global warming will be less than is currently predicted," Bradford said, "even a small change in atmospheric carbon is going to alter the way our world works and how our ecosystems function."

The role of microbes in nature

By Sara Hallin and Rolf Bernander

Six research groups from Uppsala Microbiomics Centre (UMC) at the Swedish University of Agricultural Sciences and Uppsala University are busy developing tomorrows tools for the study of the ecology of microbial communities. The key task is to identify microbes and to link them to particular functions.

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The role of microbes in nature

Facts

Uppsala Microbiomics Center

UMC consists of six groups of researchers with eight senior researchers, 5 postdocs and 4 postgraduate students.

Microbes make up most of the biodiversity on Earth, and several of the processes which microorganisms perform are of critical importance for the cycling of nutrients, the degradation of various compounds, and the global climate. Knowledge of microbes in the environment helps mankind to develop ecosystem services and to find strategies to utilise our agricultural natural resources in a long term sustainable manner.

A driving factor for deeper understanding has been the technological revolution which environmental microbiology has undergone over the past 10 year period, with new methods to identify and count microorganisms in the environment opening up an entirely new world. Discoveries of new groups of organisms with previously unknown properties have rapidly increased. We are however only just beginning to understand how microbial communities can be linked to various functions in ecosystems, and new interdisciplinary approaches are important in advancing research in environmental microbiology.

Strong research environment

A number of research groups at Swedish University of Agricultural Sciences (SLU) at Ultuna and Uppsala University (UU) recognised the need to develop methods and theories to understand the dynamics, composition and function of microbial communities in land and water. The ideas found support at Formas, and Uppsala Microbiomics Center was allocated support as a "strong research environment".

UMC is coordinated by Professor Janet Jansson at the Department of Microbiology, SLU, now at Lawrence Berkely National Laboratory in California, and since this year by the deputy coordinator Sara Hallin at SLU.

The strength of UMC is that the network unites researchers, who are working with microorganisms from all three domains of life, i.e. Bacteria, Archaea and Eukarya, both in terrestrial and aquatic environments, with groups who are specialised in protein chemistry and micromechanics (see the box). The main objective of UMC is to develop and apply new methods to analyse and characterise entire microbial communities and individual species, in order to understand their ecology and significance for agriculture, forestry and the environment.

Carbon and nitrogen cycling

Technical development is driven on several fronts. The researchers chiefly focus on developing advanced biomarkers to study active proteins in the environment, as well as new tools at microscale, e.g. cell sorting directly in the field. The latter is based on microfluidic techniques and may be used to separate single cells or specific organisms from a complex system. Experiments have also been made for the rapid diagnosis of the composition of bacteria in complex samples using chip based methods. The new techniques are now being integrated into ongoing research in which the researchers are focusing on a number of key issues in the cycling of carbon and nitrogen, with the aim to describe what microbes are involved and who does what.

Chitin

The groups are engaged on a joint project in which the microorganisms involved in the degradation of chitin are studied. Chitin is the second most common biopolymer in the biosphere and is an important source of carbon and nitrogen in nature. Degradation is thus important, inter alia for the growth of conifers in nitrogen-deficient forest soils. Chitinases, which are the active component in degradation, exist in a large number of variants, and it is not clear which of these are active in different ecosystems and how they can be linked to specific groups of microorganisms. The researchers have recently finished work on mapping the relationships among different chitinases and developing biomarkers for studying them in the environment. Plans are now being made for a major study of chitinases in different ecosystems.

The climate is affected

Other areas in which the research groups are interested are the significance of microorganisms for the inflow of carbon dioxide into environments poor in carbon, as well as new organisms and enzymes involved in nitrogen cycling between ecosystems and the atmosphere. Research on carbon sequestration and nitrogen turnover helps us answer fundamental ecological questions of great interest, and can also provide new information that is of critical importance for the global climate. Intensive research is in progress to investigate the role of Archaea for these processes. It is commonly assumed that Archaea are primarily found in extreme environments such as hydrothermal vents or seas of extreme salinity, but research shows that they are likely to be of major importance in the cycling of both carbon and nitrogen in non-extreme ecosystems.

National competence centre

After its inception, UMC has generated further grants and resources, and attracted visiting researchers and post-docs from different parts of the world. International courses are regularly arranged, as well as conferences and seminars. UMC is now building up a national resource and competence centre for a broad spectrum of issues concerning microbiology and microbial ecology, in order to enhance readiness and prospects for the climatic, energy related, agricultural and environmental issues of the future. The centre is continually developing as new methods and knowledge become available, and UMC invites both researchers and the public to contact the network members for collaborations or to pose questions related to this fascinating and rapidly expanding field.

Climate change and microbes: influence in numbers

Microbes, it is safe to say, are sadly neglected in most discussions of climate science. Under our noses, but mostly invisible to the naked eye, these tiny organisms are easily overlooked. And yet there is nothing we human beings can do from one minute to the next that is not based on co-operative arrangements with our microbial partners. Our respiration, digestion, immune function, wellbeing and overall survival depend on microbes. All our food is produced in alliance with complex communities of the organisms, as are many other life-sustaining materials. In fact, 90% of the cells in our bodies are microbes, and 99% of the genes in our bodies reside in these microbes. Most of these microbes live in our digestive tract although they are also found on the skin and in all our bodily cavities.

Crucially, microbes have the capacity to alter the environment in profound and lasting ways. Historically they are the most effective geoengineers and biogeochemists. Life as we now know it could not have evolved without the dramatic rise in oxygen levels - the Great Oxidation Event - some 2.3billion years ago. Although the causes of this relatively sudden increase in atmospheric oxygen remain shrouded in controversy, it is widely agreed that cyanobacteria in the oceans were the first organisms to produce oxygen: there is little doubt that these microbes played a major role.

Today, at any rate, microbes are the drivers of the oxygen cycle and an essential part of the nitrogen cycle. Before the development of the human chemical industry, microbes were the only agents capable of fixing atmospheric nitrogen for the chemical needs of higher plants and animals.

Changing times

Microbes could have various positive and negative feedback responses to temperature change, but the magnitudes of these are inadequately understood. This lack of knowledge is probably the reason why microbial activity is missing from most climate change models. Regardless of the reasons for this neglect, climate change models that fail to factor in microbial activities are manifestly inadequate.

Microbial decomposition of organic matter is crucial to the terrestrial carbon cycle. The same goes for the oceanic carbon cycle; simply put, microbes dominate. Some 93% of the Earth's carbon dioxide is stored in the oceans, and oceans cycle about 90billion tonnes of carbon dioxide per year, dwarfing the 6billion tonnes or so generated by human activities. The mechanics of this oceanic carbon cycle are dominated by micro-, nano-, and picoplankton, including bacteria and archaea.1

Also crucial, but even less well understood, is the impact of marine viruses. There are estimated to be 4 1030 viruses in ocean waters, but such large numbers are unimaginable for most of us. We can try to picture the scale differently: if stretched end to end, marine viruses would span 10million light years. That's still pretty unimaginable. How about this: viral carbon is equivalent to the carbon in 75million blue whales.

So those are the big numbers, but what is the impact of these viruses? Viruses may lyse, or break open, up to 50% of oceanic bacteria per day. In this way they significantly affect geochemistry on a global scale by altering the storage and respiration of organic and inorganic material.3 These effects may have both positive and negative impacts on the carbon cycle and global warming. Far too little is known about these processes, although progress is being made.

Take another example of microbial interaction: vast areas of Arctic and alpine tundra are warming due to climate change. As it heats up, the tundra is producing increasing quantities of methane. The main source of methane in permafrost soils is methanogenic (methane-producing) archaea, while the only known terrestrial sink is methanotrophic (methane-consuming) bacteria. The balance between these methane-generating and methane-absorbing processes is poorly understood, but since methane is a far more effective greenhouse gas than carbon dioxide, our understanding needs to improve, and quickly.

Good bug, bad bug

But the possible microbial impact on climate change isn't all bad news: there are microbial interventions that could counteract climate change.

Some areas of the ocean are poor in phytoplankton. If these areas could be enriched, newly fertilised phytoplankton could absorb huge quantities of carbon dioxide. One possibility that has been widely discussed is the seeding of the ocean with iron, which can produce huge blooms of algae. John Martin, the oceanographer who did most to promote this idea, famously remarked: "Give me half a tanker of iron, and I'll give you the next Ice Age."

The proposal is, however, highly controversial. It's very difficult to predict the effect of such an intervention on the wider ocean ecology - it could certainly be highly deleterious. What's more, the effect could be limited by rapid explosions of zooplankton populations that would feed on the phytoplankton and quickly reduce their populations to earlier levels. The important point, however, is that microbial populations can respond dramatically to environmental changes, which emphasises not only the possibilities for bioengineering, but also the potential of natural feedback loops, positive or negative, as climate changes.

There are also less contested microbial technologies which could have an indirect impact on climate change, especially in the search for alternative energy sources. There are projects to grow algae for biofuel, for example, with a typical yield 30times more than an equivalent crop such as soya. Another possibility is that cars and other vehicles could be powered by fuel cells using hydrogen generated by fermenting plant waste to produce electricity. And some have even suggested that a bioreactor fitted to the exhaust system of a car might be able to trap most of the greenhouse gas emissions, which could then be converted into additional fuel by genetically engineered algal communities.

Until now, microbes have been missing from the public debate on climate change. Why? Does bringing in microbes make the message too complicated and unwieldy? Certainly climate change is a hard sell as it is. But how much of the public message about climate change is moral as opposed to scientific? If humans feel responsible for climate change then they may take on the responsibility for behavioural change. Would balancing out the anthropogenic emphasis by including microbes in the story take away "blame" for climate change? And to whose benefit?

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