Soil Enzymology: Back to the Future.

Soil enzymes are central to ecosystem processes because they mediate innumerable reactions that have biogeochemical significance in soils. Catalase was the first enzyme detected in soils, first reported by A.F. Woods at the 1899 at the AAAS annual meeting in Columbus, Ohio. Catalase was the most widely used soil enzyme assay up till the 1940s because of its ease of use.  By the 1950s a plethora of enzyme assays had been developed with varying degrees of suitability, with a goal for use as indicators of soil fertility and microbial activity - with research leadership coming from Europe, especially eastern Europe.

In the 1950s-60s Douglas McLaren at the University of California at Berkley making novel calculations of individual cell activity and with gamma radiation; demonstrated that a very large portion of activity comes from enzymes stabilized in the soil matrix. Essentially McLaren showed that “sterile” soil could still perform enzyme mediated reactions. John Skujiņš at Utah State University coined the word "abiontic" to represent these extracellular soil enzymes. Jeff Ladd at CSIRO in Australia further developed information on spatial distribution of enzyme activity within aggregates and their location at microscales on colloid surfaces using microscopy. Richard Burns, as a young lectuer at UC Berkley, influenced by McLaren, developed a career long interest in soil enzymology; notably articulatiing a conceptual framework for the role of extracellular enzymes  in ecological functioning of soil microbial communities. M. Ali Tabatabai at Iowa State University an acknowledged pioneer for may enzyme methods and other soil biochemical methods, made a major contribution by developing procedures that quantitatively extracted products from all soils, overcoming a major problem for many prior assays. One can be assured that methods developed by this laboratory were thoroughly vetted, reliable, clearly described (including helpful comments and caveats), and quantitative.

Research tools are emerging such as mass spectrometry (MALDI-TOF/MS), microscopy, “omics”, biosensors, and  bioinformatics that provide new avenues for understanding the ecology of extracellular enzymes and manipulating enzyme expression for ecosystems services. Current research and applications includes sustainable agriculture, compositing/recycling, and bioethanol production. The importance of soil enzyme research is helping to understand the consequences of climate change on soil functions. The list is endless. In conclusion, the long history of soil enzymology based on activity is still relevant but with the advances in molecular biology, microscopy, and analytical techniques this discipline is poised to provide new insights into the functions and locations of extracellular enzymes that can be applied to solve the agricultural and environmental challenges to the 21^st Century.