Soil enzyme activity: a brief history and biochemistry as a basis for appropriate interpretations and meta-analysis

Enzyme activity as a method for soil biochemistry and microbiology research has a long history of more than 100 years that is not widely acknowledged in terms of adherence to strict assay protocols and the interpretation of results. However, in the recent past, there is a growing lack of recognition of the historic advancements among researchers that use soil enzymology. Today, many papers are being published that use methods that either do not follow exact protocols as originally vetted in the research literature or individual labs use their own method that has not been optimized for pH, co-factors, substrate concentrations, or other conditions. This is of particular concern for fluorogenic substrates and microplate methods. Furthermore, there is a lack of understanding of the origin and location of a given enzyme being studied. Notably, regardless of the enzyme, it is too often assumed that enzyme activity equals microbial activity-which is not the case for most hydrolytic enzyme assays. Because as established by Douglas McLaren in the 1950s, a considerable amount of activity can come from catalytic enzymes stabilized in the soil matrix but that are no longer associated with viable cells (known as abiontic enzymes). In summary, today, many papers are using imperfect methods and/or misinterpret enzyme activity data that at a minimum confounds cross paper studies and meta-analysis. However, most importantly, lack of historical perspectives and ignoring strict protocols cause redundancy and fundamentally undermine the discipline and understanding of soil microbiology/biochemistry when enzymology methods are used.