Chapter 7 - Humus and Enzyme Activity

Abstract

A level of extracellular enzyme activity exists in soil. Enzymes secreted by living cells during normal cell activity, leaked from extant cells, or released from lysed cells, are short-lived unless they are adsorbed by soil colloids or inglobated by humic molecules. This level of extracellular enzyme activity indicates the biological capacity of the soil for the enzymatic conversion of the substrate, which is independent of the extant microbial activity; it also has an important role in the ecology of microorganisms. The activity of enzymes associated with mineral or organic colloids is one of the various activities contributing to the overall activity of the enzyme in soil. The extraction of humus–enzyme complexes from soil in good yields is obtained with solutions employed in extracting humic substances. The intrinsically high electron density of inorganic colloids masks the enzyme reaction product, while the humus material nonspecifically adsorbs the trapping agent becoming electron-dense. Using the electron probe microanalysis overcomes these problems. The chapter analyzes that if extracellular enzymes are observed in the humified organic matter, the comparison of data from extraction–purification experiments with observations by the electron probe microanalyses may prove useful.