API ZYM assay to evaluate enzyme fingerprinting and microbial functional diversity in relation to soil processes

Soil properties, enzyme activity, and microbial functional diversity coevolve with soil processes. Consequently, activity and diversity of soil enzymes could be used for evaluating the natural processes in ecosystems and their changes but, for applied management strategies, useful cost-effective methods and synthetic indicators are required. The aim of this study was to use API ZYM (API) assay to evaluate the fingerprint of soil enzyme activity and microbial functional diversity in relation to soil processes. To strengthen the results, a parallel measurement of enzyme activities was performed with microplate-fluorometric (FA) assay. Seven soil profiles classified as Haploxeralf, located in two Mediterranean areas under xeric moisture and mesic temperature soil regimes, were selected. The Synthetic Enzyme Index (SEI) was calculated as the sum of 16 enzyme activities determined according to the two methods (SEI-API and SEI-FA). Moreover, the enzyme activities were used to assess the microbial functional diversity through the calculation of the Shannon's diversity index (H' API and H' FA). The results showed a relationship between SEI-API and SEI-FA which was described by a linear model. Moreover, a significant linear regression was also found between the Shannon's diversity indices calculated according to the two methods, H' API and H' FA. Significant differences were found from surface A to deep Bt genetic horizons in a decreasing gradient of enzyme activity and microbial functional diversity. For subsurface horizons, the SEI-API was significantly higher in E than AB horizons, suggesting that API method can detect the different biochemical behaviour in eluviation processes occurring in Haploxeralfs. API ZYM assay proved to be suitable for a general biochemical evaluation and for assessing microbial functional diversity in soils of different origin, composition, and land uses. For this reason, it can be proposed as a simple cost-effective method to use during the soil survey.