Protein As the Dominant Form of Soil Organic Matter: More Questions Than Answers About the Role of Enzymes in Soil.

Enzymes are well known drivers of most biological reactions. Considerable research has been conducted to understand C-N cycling via the use of soil enzyme activity assays, however, less is known about the direct and indirect role played by enzymes in soil organic matter formation. It is thought that peptides and proteins compose a large fraction of soil organic matter (30 to 60%), and since much of microbial biomass is composed of proteins (5-25% protein in cytoplasm), it is expected that enzymes would be an important contributor to the accumulation of organic matter in soil. While proteins are readily degraded in solution by microbial-derived proteases, there accumulation in soil can be explained by mechanisms of protection, which remove proteins from microbial proteolytic attack. Indeed, when proteins are added to soils, they are not easily recovered. Proteins are also well known to adsorb to soil minerals, which may decrease their accessibility to enzymatic degradation. Research from our laboratories indicate that amino acid sequence is an important factor determining the recovery of peptide-proteins mixed with soil minerals. The type of mineral also determines whether most or little of the peptide-protein can be recovered, using current extraction methodologies. Many questions remain about the role that proteins and enzymes play in both the degradation and accrual of organic matter in soil. The presentation will describe both research results and the current direction of research taken by ourselves and others studying soil proteins.