Soil Amendments with Lignocellulosic Residues of Biorefinery Processes Affect Soil Organic Matter Accumulation and Microbial Growth

The development of soil microbiota and the chemical composition of soil organic matter (SOM) were studied in a 180 day incubation experiment upon addition of a characterized lignocellulosic biorefinery residue (BYP) at two different rates. The microbial growth was studied by PLFA analysis after 30, 60, and 180 days, while SOM molecular composition was assessed by thermochemolysis at the end of the trial. Soil amendments with BYP induced a well differentiated microbial community. However, the overall microbial development significantly decreased over the experimental time due to a lesser availability of decomposable C to microorganisms. The reduced C accessibility was related to the progressively higher SOM recalcitrance with increasing BYP rates and was attributed to selective accumulation into the stable SOM fraction of hydrophobic compounds which prevented further BYP mineralization by protecting BYP from microbial activity. Our findings indicate that amendments with lignin-rich residues from biorefinery processes may promote the stabilization of humified molecules in soils, thus leading to a net C accumulation in soils.