Ecological Indicators 13 (2012) 322–327 Contents lists available at ScienceDirect Ecological Indicators jo ur n al homep ag e: www.elsevier.com/locate/ecolind -Glucosidase kinetic parameters as indicators of soil quality under conventional and organic cropping systems applying two analytical approaches M.C. Moscatelli a,∗ , A. Lagomarsino b , A.M.V. Garzillo c , A. Pignataro a , S. Grego d a Department for Innovation in Biological, Agro-food and Forest systems, University of Tuscia, Viterbo, Italy b Agriculture Research Council (CRA), Research Centre for Agrobiology and Pedology (CRA-ABP), Firenze, Italy c Department of Ecological and Biological Sciences, University of Tuscia, Viterbo, Italy d Department of Agriculture, Forests, Nature and Energy, University of Tuscia, Viterbo, Italy a r t i c l e i n f o Article history: Received 23 January 2011 Received in revised form 14 June 2011 Accepted 28 June 2011 Keywords: Soil quality indicators -Glucosidase Enzyme kinetics Ka Spectrophotometry Fluorimetry Soil management a b s t r a c t Soil enzymes are widely used as indicators of soil quality because they are sensitive to various land management practices. In particular, enzyme kinetic behaviour and the derived kinetic parameters (V max and K m ) can be indirectly influenced by changes of soil structure, organic matter quantity and quality due to the addition of organic amendments to the soil. When measuring enzyme kinetics, the calculation of the specificity constant (K a ), i.e.: the ratio V max to K m , is advisable to obtain additional information on the whole catalytic process. Many assays for a wide range of soil enzymes have been set up and they differ for the substrate used, incubation conditions and detection methods: the most widely used are those based on spectrophoto- metric and fluorimetric techniques. However, the comparative information between the two assays is poor. Therefore this study aimed to answer the following questions: (1) Can -glucosidase kinetic parameters be considered reliable indicators in detecting changes due to soil management? (2) Can the specificity constant (K a ) be considered an additional kinetic parameter useful as a new ecological indicator? (3) Do different analytical approaches give the same results? Both experimental approaches, fluorimetric and spectrophotometric, were effective in highlighting changes occurred under organic and conventional management indicating higher level of enzyme (V max ) under organic cropping system. However the specificity constant (K a ) demonstrated that organic management did not affect the whole catalytic behaviour of -glucosidase. On the other hand, as regards the two analytical approaches, K a increased significantly using the fluorogenic substrate, 4-MUF--d-glucopyranoside, indicating a higher catalytic efficiency of the enzyme with the fluorimetric approach. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction Enzyme activities are widely used as reliable soil quality indi- cators (Dick et al., 1996). There is currently great interest in the use of extracellular enzymes as biological indicators of soil qual- ity, as they are closely related to important soil properties such as content of organic matter, soil physical properties, as well as microbial activity or biomass. Soil enzymes have therefore ecolog- ical significance, are sensitive to environmental stress and respond rapidly to changes in land management (Dick, 1997). In partic- ular, they have been increasingly used to investigate changes in functions due to anthropogenic impacts (Bandick and Dick, 1999; Kandeler et al., 1999; Naseby and Lynch, 2002; Moscatelli et al., ∗ Corresponding author. Tel.: +39 0761 357329; fax: +39 0761 357242. E-mail address: mcm@unitus.it (M.C. Moscatelli). 2005). In agricultural soils, under different organic amendments, differences in microbial biomass and microbial activity may in fact influence nutrient availability to crops (Lagomarsino et al., 2008a) stimulating microbial synthesis of enzymes involved in nutrient transformations (Melero et al., 2006; Lagomarsino et al., 2008b). Michaelis–Menten kinetic parameters can be used to differ- entiate between enzyme sources and because they are sensitive to various land management practices (Nannipieri and Gianfreda, 1998; Knight and Dick, 2004; Nourbakhsh and Monreal, 2006). Enzyme kinetic parameters and their relative efficacy were used as indicators of changes in soil quality (Masciandaro et al., 2000; Marx et al., 2001). Determination of enzyme kinetic parameters, rather than the simple activity measurement, is important to gain some knowledge on soil enzyme kinetics at least for three fundamental reasons: (i) kinetics provides valuable information on the mecha- nism of action of an enzyme; (ii) it can give an insight into the role of an enzyme under specific soil conditions and the response of the 1470-160X/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ecolind.2011.06.031