**1. Introduction**

The main purpose of the chapter is clarify description of the role of intracellular enzymedehydrogenase in the soil environment, as well as presentation of soil factors, influencing an enzymatic activity, by either stimulation or inhibition effect on soil dehydrogenase activity (DHA).

The most common laboratory procedure used for DHA determination is the method developed by Casida et al. (1964). According this method, specific dyes such as the triphenyltetrazolium chloride (TTC), that can specify the flow of electrons are useful indicators of electron transport system (ETS) activity. By the reduction of colorless, water soluble substrate (TTC) by dehydrogenases present in the soil environment, an insoluble product with red color (triphenylformazan-TPF) is formed. TPF can be easily quantified calorimetrically at the range of visible light (485 nm). This test however, reflected positive answer only at neutral range of pH and in presence of calcium carbonate for buffering soil system. Briefly, if the red colors of soil samples prepared for spectrophotometer analyses are more intensive, the measured level of DHA is higher. Consequently, soil samples without red colors or those with light red colors are characterized by lower DHA values.

Determination of DHA in the soil samples gives us large amount of information about biological characteristic of the soil. It was confirmed that although oxygen and other electron acceptors can be utilized by dehydrogenases, most of the enzyme is produced by anaerobic microorganisms. In other words, soil DHA strongly increases under anaerobic conditions.

Several environmental factors, including soil moisture, oxygen availability, oxidationreduction potential, pH, organic matter content, depth of the soil profile, temperature, season of the year, heavy metal contamination and soil fertilization or pesticide use can affect significantly DHA in the soil environment. In the current chapter we would like to concentrate on precise description of mentioned factors effect on soil DHA level. Presented

© 2012 Wolińska and Stępniewska, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

results of laboratory experiments were conducted on different soil types, representing dominant types of arable soils in Poland, in order to demonstrate changeability and variability of DHA at diverse soil environment.

Dehydrogenase Activity in the Soil Environment 185

**0 1,5 2,2 2,7 3,2**

Life in the soil environment, as well as land use is related to alternate cycles of humidification and drainage (Wolińska & Bennicelli, 2010). Water availability strongly affects on soil microbial activity, community composition (Geisseler et al., 2011), and consequently on soil enzymatic activities. As soils dry, the water potential increases, and as well microbial activity as intracellular enzyme activity slows down (Geisseler et al., 2011). In the case of wet soils, increased moisture could bring into soil solution soluble OM, what might be responsible for increase of bacterial population number (Subhani et al., 2001). What is important, we should have consciousness that any compound, which alters the number or activity of microorganisms, could on the other hand affect on soil biochemical properties, and ultimately also on soil fertility and plant growth (Subhani et al., 2001).

A basic hydrophysical characteristic of soil is water retention, that can be described as a dependence between soil water content and soil water potential. Soil water content in the function of the soil water tension is described by pF curve, which provides information about the ability for water retaining by the soil pores at any given water tension, or conversely, how

The Figure 1 demonstrates diminishing trend for DHA behaviour at different soil moisture, described as water potential values. During this experiment gig set of soils (n=315), including all representatives among the most typical Polish mineral soils (*Eutric Cambisol*, *Eutric Histosol*, *Eutric Fluvisol*, *Mollic Gleysol*, *Orthic Podzol*, *Rendzina Leptosol*, *Haplic Phaeozem*) were investigated. However, each of soil unites displayed DHA reducing trend with increase of soil pF value, what means that maximum values of DHA in the soil profiles

**(0-30cm) (30-60cm) (60-100cm)** 

**Figure 1.** DHA (µgTPFg-1min-1) dependence from water potential (pF) at different mineral Polish soil

**0 1,5 2,2 2,7 3,2 pF** 

**0 1,5 2,2 2,7 3,2**

Statistical relationships between DHA and soil water content, described as pF value in the range of pF0 – pF3.2, determined by Wolińska & Bennicelli (2010) are presented in Table 1.

Founded significant negative relationships between DHA and pF are confirmed by our above mentioned observations, that DHA is strongly affected by soil moisture. These strong

tightly a water is held between soil aggregates (Wolińska & Bennicelli, 2010).

are indirectly connected with maximum soil moisture (pF 0).

types, during reoxidation (n=315), according to Wolińska (2010)

**3.1. Soil moisture** 

**DHA (µgTPFg-1min-1)** 
