Nahaufnahme Erde

An average of 100 billion microorganisms and (tens of) thousands of different species live in one gram of soil.

Hid­den Diver­sity

A single gram of soil contains more organisms than the total number of people on Earth. The significance of microbial diversity in soil and its impact on climate change are central to microbiologist Nadine Präg's research.

"Microorganisms play an essential role in the soil. Around 100 billion microorganisms live in one gram of soil. Without these microorganisms, organic matter would cease to decompose, mineralization would halt, and, within a few decades, primary production, including plant growth, would stop," says Nadine Präg, Senior Scientist at the Department of Microbiologyat the University of Innsbruck, elucidating the importance of her research area. Her work primarily examines the effects of climate change on soil microorganisms, as the soil ecosystem responds in a complex and sensitive manner to external changes like drought or warming. According to Präg, soil dynamics are extremely complex, making the precise outcomes of stress factors challenging to predict. Surprisingly, extreme conditions such as drought or heat can increase microbial diversity – a finding contrary to initial expectations. While this might initially seem positive, the increase in diversity is often linked to recurring climate disturbances, complicating the assessment of changes in diversity.

"A higher diversity is not necessarily positive, as in some ecosystems, key organisms can be sufficient to maintain a functioning system," Präg adds. "The soil's structure offers an infinite variety of habitats and thus harbors an immense species diversity, making it the most species-rich singular habitat on Earth. One thing is clear: anyone concerned with climate change must also consider microorganisms," Präg asserts.

Climate-Effective Microorganisms

Microorganisms decisively influence the climate by releasing and consuming gases critical to global warming. For instance, some microorganisms are involved in the production and reduction of methane, the second most significant greenhouse gas after CO2. Nadine Präg has extensively studied the interaction between methanogenic (methane-producing) and methanotrophic (methane-consuming) microorganisms. "This dynamic interplay is especially relevant concerning climate change and how temperature variations may affect the methane cycle in soil," explains Präg. Notably, methanogenic organisms are archaea, a group that was only identified as distinct around 50 years ago. The realization that archaea are a separate group has unveiled new avenues of research and the opportunity to delve into their specific roles in the soil.

Their function as methane emitters is crucial for understanding both the methane cycle and the impact of land use on this cycle. "Methane-producing archaea thrive in oxygen-deficient, compacted soils. Common habitats with these conditions, where methane is produced in large quantities, include wetlands, rice paddies, and the digestive systems of ruminants. Conversely, methanotrophic microorganisms, which are the sole biological sink for methane, require oxygen and are typically found in well-aerated forest soils," Präg clarifies. In typical grassland soils, these two groups coexist in different strata, with the methanotrophs in the oxygen-rich upper layers oxidizing methane from the layers below, thus reducing net methane emissions. Soil management practices, especially fertilization, can therefore affect the activity of both methanogens and methanotrophs. "The balance between these two groups is crucial for regulating the methane cycle in the context of climate change," Präg notes.

General Overview - The Alpine Microbiome

In microbiology, the diversity of microbial life is a key topic that has come increasingly into focus due to methodological advancements. Modern techniques allow researchers like Nadine Präg to explore this diversity, despite the fact that most soil microorganisms cannot be cultured. "These studies enhance our understanding of microbial diversity, which is relatively uncharted compared to the well-documented diversity of plants and animals," states Präg.

Through the "Microvalu" project, she collaborates with colleagues at the Department of Microbiology, as well as botanists and zoologists, to decipher the interactions among all microorganisms in the soil and those that associate with plants or are transmitted by animals. In a holistic approach, they aim to map a common microbiome encompassing all soil microorganisms, including those of grazing animals, soil fauna, and plant roots. With funding from the Austrian Science Fund FWF, the team is investigating how microbial communities change in relation to soil properties such as organic content, moisture, the diversity of animal communities, or altitude. "Understanding how altitude affects soil interactions can also help us predict how a shifting climate might influence microbial biodiversity and soil health in the future," Präg concludes, who is in the process of finalizing the analysis of data from the project.

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