Abstract
Soil storage method may alter enzymatic activity being storage conditions of the soil samples prior to analysis decisive for the results. Studies made on freshly collected soils are generally preferred. However it is always not possible due to practical reasons since for example sampling is often restricted to short period of the year or because a great quantity of microbiological analyses must be made on time and by few people. On this context, soil storage methods are needed, being cold at 4°C the most widely used although sometimes alternative storage methods are also utilized. The aim of this study is to evaluate the effect of two alternative storage methods of soil samples (freezing at –20°C and air drying conservation methods) in comparison to cold at 4°C on the enzymatic activities (dehydrogenase, phosphatase, β-glucosidase and urease soil enzymes). Samples of two forest ecosystems (pine and holm oak forest stand) were taken in two different season of the year (winter and spring 2009). Results showed that enzymatic activities differed when freezing or air drying conservation methods were used in comparison with cold soil samples. Generally, alternative soil storage methods presented lower enzymatic activity than cold at 4°C. However, these changes depend on season and sampling location.
Highlights
Soil quality depends on a large number of physical, chemical, biological, microbiological and biochemical properties, the last two being the most sensitive since they respond rapidly to changes (Dick and Tabatabai, 1993; Trasar-Cepeda et al, 1998; Ros et al, 2003; Bastida et al, 2008)
We focused our sampling on this horizon because a large portion of microbial activity occurs in these horizons, and the effects of tree species should be strongest within it. 27 soil samples were randomly collected from the pine forest stand (Fig. 2) and 18 soil samples were randomly collected from the holm oak forest area (Fig. 3) in spring 2009
In the case of the β-glucosidase enzyme, air drying conservation method significantly reduced the enzymatic activity in winter and spring whereas freezing at –20°C only decreases enzymatic activity in spring (Fig. 4)
Summary
Soil quality depends on a large number of physical, chemical, biological, microbiological and biochemical properties, the last two being the most sensitive since they respond rapidly to changes (Dick and Tabatabai, 1993; Trasar-Cepeda et al, 1998; Ros et al, 2003; Bastida et al, 2008). Among the parameters related to the biochemical and microbiological state of the soil, important are the indicators of the soil microbial activity, principally different enzymatic activities, both related to the cycles of N, P, and C (urease, phosphatase, and β-glucosidase, respectively) and of a more general nature, such as dehydrogenase and respiration These soil parameters are sensitive indicators of soil quality (Bastida et al, 2008) and could have implications for the establishment of native plant communities and cover (Vance and Entry 2000). Several research works have focused on the measurement of enzyme activities and microbial biomass in forest soils (Caldwell, 2005; Lucas-Borja et al, 2010a,b) On these studies, biochemical and microbiological parameters are calculated following an established procedure nothing is argued in relation to how soil samples have been kept. The reason seems to be related with the fact that a new environment (temperature, humidity, etc.) is created when soil samples are collected and stored (Mondini et al, 2002; De Nobili et al, 2006)
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