Soil bioenergetics

Soils store the largest pool of carbon in the terrestrial biosphere and contain more than double the amount of carbon in the atmosphere. Yet, soil processes remain a partly missing piece in our understanding and predictive capability of the soil’s response to climate change and feedback thereof on climate. The biogeochemical cycling of carbon in soils is tightly coupled to the metabolic activity of microorganisms: heterotrophic microorganisms use soil organic matter (SOM) as an energy source by oxidizing organic carbon and transferring the released electrons onto terminal electron acceptors. Under conditions where the microbial energy investment exceeds energy gain, SOM may accumulate due to bioenergetic constraints on microbial activity. Electron transfer reactions and associated energy transformations can therefore be considered the universal currency driving the biogeochemical cycling of carbon.

In this project, we explore how bioenergetic constraints on microbial activity affect the transformation and persistence of SOM. We aim to assess changes in the chemical structure and energy properties of SOM during microbial processing. We hypothesize that bioenergetic constraints on microbial activity result in the preferential microbial utilization of less reduced, less energy-rich organic compounds under anoxic conditions. Consequently, we expect the accumulation of relatively more reduced, more energy-rich organic compounds that preferentially associate with soil minerals due to their relatively lower hydrophobility under anoxic compared to oxic conditions. We will test our hypotheses in a series of laboratory incubation experiments and mesocosm experiments in the field using methods such isothermal calorimetry, as well as mass spectrometry approaches.