Carbon preservation in soils: The role of carbon chemistry in soil aggregate formation

To mitigate climate change, it is of vital importance to increase the stocks of global soil organic carbon (SOC), which also improves soil resilience, soil fertility and thus food security. 

The preservation of SOC heavily depends on its vulnerability to microbial degradation. Two processes and their interplay strongly influence carbon protection: the formation of primary organo-mineral (O-M) complexes via the sorption of dissolved organic carbon (DOC) to fine-grained soil minerals, and the aggregation of these to form micro and macroaggregates. To date, research suggests that the chemistry of the SOC and the mineralogy of the soil matrix play a key role in the formation of O-M complexes and their stability against microbial degradation, but whether and to what extent these factors help control micro and macroaggregation are unknown. 

We focus our investigation on how the chemistry of the SOC source affects the stability and aggregation of iron (oxyhydr)oxide O-M complexes. Thus, we determine the sorption behaviour of different SOC sources chosen to represent different functional group chemistries, using sorption isotherm experiments and electrophoretic techniques. We also conduct long-term aggregation experiments to track aggregate particle size using a novel Particle Size and Shape Analyzer technique.  

Our findings suggest that the stability and aggregation modes of O-M complexes are a function of SOC chemistry, and that aggregation patterns are strongly influenced by the presence of microbial exudates and communities.