**5. Conclusions**

202 Dehydrogenases

deviations are presented

2005).

**Figure 14.** The variations of DHA in *Haplic Luvisol* at different Cr (III) and Cr (VI) concentrations (according to Stępniewska & Wolińska, 2005). Averaged values of three replicates with standard

Non-amended soil samples were used as a control, and their enzymatic activity were estimated as 100%. Effect posed by Cr content was calculated as a decrease of its level, in relation to the control value. We found that the lowest values of DHA were the effect of increasing Cr(III) and Cr(VI) doses. *Haplic Luvisol* seemed to be very sensitive on Cr contamination. DHA was reduced to 18-20% in the samples enriched in Cr (III) forms. Surprisingly, the more dangerous form of Cr (VI) was less harmful for DHA in the *Haplic Luvisol*, because enzymatic activity remained on the level of 84%, with a 1µg kg-1 addition and decreased to the value of 14% with the highest supplement of Cr (VI). One possible explanation for this fact is that. the more dangerous form of Cr (VI) was reduced to the less toxic form of Cr (III) by microorganisms, living in the soil (Stępniewska & Wolińska,

**B**

In the same way we investigated effect of Cr forms on *Eutric Cambisol* (Stępniewska & Wolińska, 2004). Received results are shown in Fig. 15. We stated that excess of Cr forms in soil disturb homeostatic metabolism of microbes, what reflect their enzymatic activity. DHA demonstrated a tendency to decrease with increase of Cr concentration. The lowest content of both Cr (III) and Cr (VI), at the level of 2 mg kg-1 reduced soil DHA to 51-66%, respectively. But at the same time the highest Cr (III) and Cr (VI) supplement at the level of

Inhibition of DHA by applied Cr compounds was also reported by Wyszkowska et al. (2001), who noted that decrease of enzymatic activity in soil should be considered as very unfavourable in terms of soil fertility, because soils of good quality and high content of soil

The decrease of soil DHA by several metallic elements (Al, Be, Cu, U) was also discussed by Antunes et al. (2011), whereas a study by Nowak et al. (2002) found that DHA decreased by

20 mg kg-1 limited DHA to 6-15%, in relation to the control.

OM show high enzymatic activity.

up to 85% at 5 mM selenic acid (IV) presence.

Soil is a part of the terrestrial compartment, and supports all terrestrial life forms. Thus, without proper soil protection policies, numerous problems may arise, like reduction of soil fertility, erosion, groundwater contamination, insufficient water holding capacity and loss of biodiversity. To asses soil quality, it is essential to measure all potential changes in biological soil properties, because they are highly sensitive to any environmental perturbations and stresses. A usual approach to diagnose soil quality, is to use a soil microbial indicators, which are very sensitive and respond quickly to environmental alterations.

Among different soil indicators, DHA is one of the most adequate, important and one of the most sensitive bioindicators, relating to soil quality and fertility. Moreover, their routine measurement is simple and low-cost under laboratory condition. However, we should not remind about limitations, resulting from laboratory conditions, when we are able to measure and estimate only potential DHA, similarly like we are able to cultivate only small percentage of soil microorganisms, on artificial media.

Soil enzymes are strongly associated with microorganisms. Soil enzymatic activity plays an important role in catalyzing reactions indispensable in life processes of soil microorganisms, decomposition of organic residues, circulation of nutrients, as well as forming organic matter and soil structure. Thus, it is possible to say that without proper soil enzymes system, soil life processes will be disturbed.

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 humic molecules.

Dehydrogenase Activity in the Soil Environment 205

preferred by soil microorganisms), analogically like increase of temperature to 30°C (temperature close to optimum for microorganisms growth and development) resulted in

Presented and discussed above results are based on our several years studies, however additional investigations are needed and recommended to determine the relative contribution of the different environmental effects on soil DHA. However, the discussion highlights the strong interactions between the soil environment, soil enzymes

The study was partly funded by Polish Ministry of Science and Higher Education (grant N

Agnelli, A.; Ascher, J.; Corti, G.; Ceccechrini, M.; Nannipieri, P. & Pietramellara, G. (2004). Distribution of Microbial Communities In a Forest Soil Profile Investigated by Microbial Biomass, Soil Respiration and DGGE of Total and Extracellular DNA*. Soil Biology &* 

Andrea, M.; Peres, T.; Luchini, L.; Bazarin, S.; Papini, S.; Matallo, M. & Savoy V. (2003). Influence of Repeated Applications of Glyphosate on Its Persistence and Soil

Antunes, S.; Pereira, R.; Marques, S.; Castro, B. & Gonçalves, F. (2011). Impaired Microbial Activity Caused by Metal Pollution: A Field Study In a Deactivated Uranium Mining

Bennicelli, R.; Szafranek-Nakonieczna, A.; Wolińska, A.; Stępniewska, Z. & Bogudzińska, M. (2009). Influence of Pesticide (Glyphosate) on Dehydrogenase Activity, pH, Eh and Gases Production In Soil (Laboratory Conditions). *International Agrophysics*, 23, pp. 117-

Błońska, E. (2010). Enzyme Activity in Forest Peat Soils. *Folia Forestalia Polonica*, 52, pp.20-25. Brzezińska, M. (2006). Impact of Treated Wastewater on Biological Activity and Accompanying Processes in Organic Soils. *Acta Agrophysica*, 131, pp. 1-163 (in Polish

Brzezińska, M.; Stępniewska, Z. & Stępniewski, W. (1998). Soil Oxygen Status and

Dehydrogenase Activity. *Soil Biology & Biochemistry*, 30, pp. 1783-1790

DHA stimulation.

**Author details** 

**Acknowledgement** 

305 009 32/0514).

**6. References** 

122

(dehydrogenases especially) and soil microorganisms.

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

Bioactivity. *Pesquisa Agropecuaria Brasileira*, 38, pp. 1329-1335.

Area. *Science of the Total Environment*, 410, pp. 87-95

Agnieszka Wolińska and Zofia Stępniewska

*Biochemistry*, 36, pp. 859-868

with English Summary)

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 metabolism.

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

In the presented chapter we described the most important soil parameters, affecting DHA, which poses ability either for stimulation or inhibition its activity.

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 contamination with heavy metals.

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 correlation coefficient (r=-0.70\*).

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 indirectly linked with DHA.

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 preferred by soil microorganisms), analogically like increase of temperature to 30°C (temperature close to optimum for microorganisms growth and development) resulted in DHA stimulation.

Presented and discussed above results are based on our several years studies, however additional investigations are needed and recommended to determine the relative contribution of the different environmental effects on soil DHA. However, the discussion highlights the strong interactions between the soil environment, soil enzymes (dehydrogenases especially) and soil microorganisms.
