The key to long-term CO2 storage in the soil: Microbial interactions stabilize carbon in the soil

Soils play a major role when it comes to the long-term storage of CO2 and the resulting reduction of this gas in the atmosphere – therefore they can contribute to slowing down climate change. In order to gain a better understanding of these mechanisms, it can be helpful to look at the microscopic level of soil microorganisms. An international and interdisciplinary group of researchers has examined how microorganisms interact with each other to contribute to the decomposition and storage of carbon in terrestrial ecosystems.

Ingrid Kögel-Knabner

Johannes Lehmann

Carbon is the most important element for all life forms on earth; it is circulating between the atmosphere, oceans and land ecosystems in the so-called carbon cycle. While a single carbon atom (as CO2) remains in the air for an average of three years before being chemically bound and converted to biomass by plant photosynthesis, it takes 23 years on average for a carbon atom in the soil organic matter to be released into the atmosphere as CO2 through microbial decomposition of dead biomass.

This microbial decomposition, however, leaves a part of the carbon in the soil, where it can be bound for a very long time – researchers estimate that they can stay in deep soil layers for hundreds, possibly thousands of years. The mechanisms responsible for this highly efficient “retention” have recently become subject to great public interest and soil scientists from all over the world are performing intensive research in this regard.

Soil conditions are continuously changing

An interdisciplinary consortium of experimental scientists from the fields of soil science and mathematical modelling lead by Johannes Lehmann from Cornell University has presented a new concept of soil-based carbon stabilization that acknowledges the fact that microorganisms live inside a highly complex environment on a miniscule scale. On several occasions, Johannes Lehmann was received as a guest at the Institute for Advanced Study of the Technical University of Munich (TUM-IAS) in the course of his Hans Fischer Senior Fellowship. The consortium’s findings were published in “Nature Geoscience”.

“The amount of carbon that microorganisms can decompose or turn into biomass for long-term storage not only depends on the amount of carbon and the sum of all microorganisms in the soil; the probability with which a microorganism and an organic carbon compound even cross paths in this microscopic environment in the soil is another very important factor. If there is a highly uneven spatial distribution of microorganisms and carbon in the soil, chances increase that a carbon molecule ends up isolated – it will therefore not be decomposed,” explained Ingrid Kögel-Knabner from TUM, the final author on the paper.

“Soil conditions are undergoing continuous change,“ said Johannes Lehmann, the first author on the study. “Even though there may be a high supply of carbon as biomass residues, microorganisms starve, especially when they have to adapt to constantly changing conditions within a maze,” he added.

The full press release can be found here.