The Importance of CO2 Utilizing Chemolithoautotrophic Microorganisms for Carbon Sequestration and Isotope Signatures of SOM in Tropical Rainforest Soils

Abstract:

Soil organic matter (SOM) is a major compartment of the tropical carbon cycle with up to 26 % of global carbon stocks stored in tropical soils. Understanding factors and processes driving SOM dynamics under changing climate conditions is crucial for predicting the role of tropical forest ecosystems to act as a carbon sink or source.

Soil microorganisms are major drivers of the belowground carbon cycle by releasing CO₂ by soil respiration but also by stabilizing and storing SOM, as indicated by recent research. Our investigations focus on chemolithoautotrophic microorganisms, a group that relies on CO₂ as their carbon source. Chemolithoautotrophic microorganisms have been shown to be highly abundant in soils, whereas their role in SOM sequestration is still poorly understood.

In tropical soils, the activity of chemolithoautotropic microbes might be important for generating and stabilizing carbon, especially in the deeper soil, which is rich in CO₂ and reduced energy sources like Fe²⁺.

They further might impact carbon isotope signatures (¹³C and ¹⁴C) of SOM, because of enzymatic fractionation during carboxylation and the use of carbon, which has a distinct isotopic composition than other carbon sources at the same depth.

In order to study the activity of chemolithoautotropic microbes and their importance for SOM, we conducted isotope and isotope–labelling studies, gas measurements as well as molecular analyses at soils from the Atto site from 0 to 1 meter depth. These soils are classified as Ferralsols and Alisols and represent the most abundant soil types in the Amazon.

With this we will be able to gain knowledge about the function and identity of an important group of microorganisms and their contribution to crucial biogeochemical cycles in the world`s most important ecosystem.