New Geological Era Anthropocene

Human activities have pushed the planet into a new geological epoch known as the Anthropocene. In this new era, climate change affects most life on Earth, making it one of the biggest challenges the world is currently facing . Although extensive research has been dedicated to its effects on various ecosystems, these studies usually concentrate on the macroscopic organisms. Less time and effort have been devoted to establishing its effects on microorganisms such as bacteria and fungi, even though it is widely established that they are important for our survival.

Microbes in the soil are essential to plant growth, nutrient recycling and especially in providing fixed nitrogen, which is usually limiting in the environment. Therefore, the effect of climate change on nitrogen-fixing bacteria must be established as the global food demand is set to double by 2050.

Bacteria and archaea are also key players in marine ecosystems where they form symbiotic relationships with algae and kelp, among others. Photosynthesis carried out by these organisms is responsible for more than half of the oxygen produced on the planet and thus, the effects of climate change on these intricate relationships must be investigated.

Furthermore, the human microbiome has been gaining attention, as scientists explore its connection to human disease and its importance on health in general. This review will therefore cover the following topics: the effect of climate change on microorganisms in soil and oceanic environments, on host-microbiota interactions and the implications for humans. The possible uses of microorganisms in fighting climate change will also be discussed briefly.

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Impacts of climate change on soil microbiota. Soil is one of the most complex and diverse ecosystems on Earth. Although the soil type and plant species present dictate the microbial abundance and diversity, bacterial counts in a gram of dry soil can be as high as 2×109 cells. Most of these bacteria are concentrated around plant roots, in an area known as the rhizosphere. Plants deposit up to 40% of photosynthetically fixed carbon via their root system, where it is used for growth by the surrounding microorganisms. This is an indicator of how important this mutual relationship is to plants, as the benefits must outweigh the major energetic costs. Increasing temperatures, atmospheric CO2, drought, precipitation and flooding are all consequences of climate change and affect the soil microbial community composition either directly or indirectly.

Elevated atmospheric CO2 has been shown to cause a drastic increase in net primary production by plants, causing an increase in plant litter, root growth, turnover and depth distributions. The response largely depends on the soil type and plant species sensitivity to carbon dioxide, but increased rhizodeposition can cause changes in microbiome composition and may lead to increased microbial decomposition of soil organic carbon. This would temporarily lead to even more carbon escaping into the atmosphere, intensifying the effects of climate change. In an experiment spanning six different terrestrial environments under elevated CO2 conditions, a common decline in Acidobacteria was observed. Acidobacteria are one of the most abundant taxonomic groups in soil making up 10-50% of some environments.

Although little is known about their exact role due to a lack of culturing techniques, they are known to survive in low nutrient and extremely polluted conditions. Sequence analysis also suggests that they play a part in terrestrial carbon cycling and are capable of degrading complex carbon sources such as hemicellulose and pectin. This capability makes them a potential candidate for biofuel production, which would relieve some of the stress placed on our planet by burning fossil fuels. Another area of concern is the compounding effect of elevated CO2 with other effects of climate change. In an Australian grassland study, elevated CO2 lead to an increase in total fungal abundance but when coupled with warming there was an overall decrease. Studying multiple variables at once is therefore an important goal for future research as many areas around the world will experience multiple effects of climate change at once.

Increasing temperature

Temperature changes influence soil microorganisms by affecting their growth rate and enzyme function. Several studies state that the effect of warming on soil microbiota is largely dependent on the mean annual temperature (MAT) in the area. Ecosystems with a lower MAT will experience a drastic increase in microbial growth and respiration following a 1°C increase in annual temperatures. Therefore, rising temperatures pose the largest risk to areas dominated by ice. It is known that permafrost contains around 50% of the global soil carbon and twice as much carbon as the atmosphere.

The response of microbial communities in these ecosystems to warming will thus determine whether these areas will become carbon sinks or pools and to what extent global carbon cycling will be affected. Permafrost thawing could double the warming from greenhouse gases and essentially make any attempts to cut back on fossil fuel use futile.  The current aim is to keep the global temperature rise below 1.5°C but even at that, the effect on certain ecosystems could be profound. The overall effect this will have on global feedback loops is still largely unknown and represents a gap in current research.

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