Six Feet Under Climate Change: What the Soil Tells Us

Norris Geyser Basin in Yellowstone National Park. The left stream's water temperature ranges between 38 and 56 degrees. The green hue is caused by heat-loving bacteria that produce their nutrients via photosynthesis. Source: Wikimedia Commons.

Norris Geyser Basin in Yellowstone National Park. The left stream’s water temperature ranges between 38 and 56 degrees. The green hue is caused by heat-loving bacteria that produce their nutrients via photosynthesis. Source: Wikimedia Commons.

Global climate change brought about by recent human activities has gathered a broad community of scientists and politicians to address perhaps one of the most important challenges of the 21st century. Political attempts to undertake actions towards climate change are limited by our ability to assess this problem. Although not often discussed in climate change conferences, soil microorganisms can be affected by and contribute significantly to climate change. Microorganisms are crucial for the terrestrial carbon and nitrogen cycles, and thus have a momentous impact on the production and consumption of greenhouse gases.

One direct major effect of climate change on soil microorganisms is the way global warming can accelerate microbial activity and this way create a positive feedback loop on climate change. For example, large quantities of carbon and nitrogen are stored in living organisms and soil, acting as natural sinks for these elements. Hastened decomposition of soil organic matter by microorganisms as an effect of global warming can increase CO2 in the atmosphere. However, the nature of this process is far from clear.

The diversity of soil organic matter and the microbial temperature dependence of organic compound decomposition makes the soil ecosystem an incredibly sophisticated system. Evidence from several studies suggests that the temperature sensitivity of litter decomposition is affected by the quality of the organic material and various microbial groups may respond differently to temperature change. To add yet another layer of complication, restraints on organic matter by different physical and chemical means in response to climate change will limit available substrate for the microorganisms and diminish their ability to respond to warming conditions.

Greenland coast. Source: Hannes Grobe, Wikimedia Commons.

Greenland coast. Source: Hannes Grobe, Wikimedia Commons.

On the other hand, the increasing frequency of extreme weather conditions related to climate change, such as drought, may have even more severe effects on microorganisms and their activities. Drought in wetlands and peatlands will increase the availability of oxygen in otherwise anaerobic soil, which affects the breakdown and the decomposition of organic matter. In addition, it can significantly increase the emission of nitrous oxide – a vigorous greenhouse gas – whose atmospheric concentration has been shown to be increasing at a rate of 0.2-0.3% per year. Similarly, climate change related decline in snow-covered land has significant importance since this makes protected organic matter available for microorganism decomposition.

Climate change can also act indirectly on soil microorganisms and affect their activities by different means. High concentration of atmospheric carbon dioxide increases plants’ photosynthetic activity, which subsequently leads to increased amounts of organic plant products in the soil. The consequences of this increase, however, have proved to be a challenge to address. Several factors can affect the outcome of this process, such as plant identity and soil fertility in addition to a multitude of other ecosystem characteristics. Climate change effects on microorganisms can also occur throughout longer time periods spanning up to centuries. Through its characteristics, such as global warming and modified precipitation, climate change has altered the composition and diversity of vegetation at both local and global scale. This led to changes in plant root architecture and more importantly changes in the quality and quantity of soil organic matter. Slow-growing plants have a low litter turnover, which is usually low in nutrients when compared to fast-growing plants that have high litter turnover. These changes can both positively and negatively influence microorganisms and their activities, confirming the complexity of climate change on soil microorganisms.

The majority of studies, including the studies mentioned above, have mainly attempted to address the effects of single determinants of climate change on soil microorganisms. This may portray the generated data as incomplete, since it fails to thoroughly examine the interactions of different factors, both in their additive and hostile forms.

A hearing in Dirksen Senate Office Building in Washington, D.C. Source: Wikimedia Commons.

A hearing in Dirksen Senate Office Building in Washington, D.C. Source: Wikimedia Commons.

The myriad of ways that climate change can affect not only soil microorganism but also countless other global properties have led to uncertainty among a few politicians. Senator James Inhofe (Republican-Oklahoma), the current chairman of the Unites States Senate Committee on Environment and Public Works has recently presented “evidence” disproving climate change and its effects. Additionally, Senator Ted Cruz (Republican-Texas), a candidate for the 2016 Unites States presidential election and the chairman of the Senate Space, Science and Competitiveness Subcommittee has criticized government endeavors on climate change in an attempt to limit climate change research.

A better understanding of climate change in general and its effects on soil microorganism in particular can disprove these uncertainties. This could be achieved by multifactorial long-term field studies, which take all relevant factors into consideration . Such studies may be conducted by interdisciplinary methods that take the entire ecosystem into account. For these reasons, soil microorganisms are bound to be included in our considerations with respect to climate change in the near and far future.