**Author details**

204 Dehydrogenases

humic molecules.

metabolism.

DHA is related to quantitative changes in microorganisms populations, as only strictly intracellular enzymes can truly reflect microbial activity, because with respect to the degradation processes of extracellular soil enzymes, they will be quickly mineralized by other enzymes (i.e. proteases), unless they are either adsorbed by clays or immobilized by

It should be also remind, that overall soil DHA level depends most of all from the activities of various types of dehydrogenases, which are fundamental part of the enzyme system of all living soil microorganisms, i.e. the respiratory metabolism, the citrate cycle, and N

Due to this fact, DHA is proposed as the best indicator of the microbiological redox-systems, and could be considered as good and adequate parameter of microbial oxidative activities in soil. Furthermore, soil DHA is also used as a measure of any soils disruption posed by pesticides, heavy metals, or other soils contaminates and improper management practices.

As DHA is strictly connected with living microbial cells, its activity depends from the same environmental factors, which influence on microorganisms abundance, activity and life processes. Consequently, when entertaining soil DHA behavior in the soil environment, we should be not only limited to DHA, but it is necessity to consider on the most important

In the presented chapter we described the most important soil parameters, affecting DHA,

To sum up the forgoing observations it was demonstrated, that DHA display increasing trend under anaerobic conditions, what suggest that the facultative and anaerobic member of soil microbial community become more important in soil respiration processes. Thus, soil DHA was reported to be negatively correlated with soil water potential, oxygen diffusion rate, and redox potential, what means that DHA reached higher values at lower soil water potential, lower oxygen diffusion rate and lower redox potential conditions. Analogically, negative correlation we also found in the case of soil depth–what was connected with spatial stratification of microorganisms abundance and its preference for inhabiting the surface layers of the soil profiles. Inhibiting effect on DHA level have also pesticides and soil

Important parameter affecting soil biological activity is pH. Our investigations demonstrated, that optimal pH range for DHA is between 5.5-5.73, what was confirmed by

Soil DHA depends also from the season of the year, similarly like dynamics of microbial activity, and reached the highest level in May, as spring season is strongly connected with increase in microbial activity, and intensification of oxido-reduction reactions, what is

Positive relationships we noted between DHA and two parameters: TOC and temperature, what means that DHA reached higher values at soils with higher TOC content (what is also

soils factors and conditions, affecting measuring by us DHA level.

which poses ability either for stimulation or inhibition its activity.

contamination with heavy metals.

correlation coefficient (r=-0.70\*).

indirectly linked with DHA.

Agnieszka Wolińska and Zofia Stępniewska *The John Paul II Catholic University of Lublin, Institute of Biotechnology, Department of Biochemistry and Environmental Chemistry, Lublin, Poland* 
