**3.3. Organic matter content**

188 Dehydrogenases

**DHA response** 

coefficient (R) (95% LSD method, n=15)

Stępniewski et al., 2000).

0.48\*\* (Wolińska, 2010).

DHA (µg TPF g-1 min-1)

Wolińska (2010)

*Rendzina Leptosols* 0-20

*Eutric Fluvisol* 0-20

**Depth**

50-60

50-60

Redox potential (Eh) is the next, important, environmental factor, which expresses the tendency of an environment to receive or to supply electrons in solution (Stępniewski et al., 2005). The well-oxygenated soils are characterized by high values of Eh (600-800 mV), in quite well-oxygenated soils Eh ~ 500-600 mV, whereas in anaerobic conditions drop of Eh below 300 mV or even lower values were observed (Pett-Ridge & Firestone, 2005;

It is well known, that Eh play a crucial role in regulating microbial activity as well as community structure (Pett-Ridge & Firestone, 2005; Song et al., 2008), and affecting on soil enzymatic activity, especially DHA. Brzezińska et al. (1998) indicated that among all aeration parameters, Eh plays the most important role in determining soil DHA level. Similar conclusions were also reported by Włodarczyk et al. (2001) and Menon et al. (2005).

We founded significant negative relationships between DHA and Eh (Fig. 4) at surface layers of *Mollic Gleysols*, *Eutric Fluvisols*, *Rendzina Leptosols* and *Haplic Phaeozems*, where determined correlation coefficients equaled as follows: r=-0.91\*, r=-0.43\*, r=-0.47\*\* and r=-

**Figure 4.** Relationship between soil DHA level and Eh at *Mollic Gleysol* (n=9, r=-0.91\*), according to

Eh (mV)

\*, \*\*, \*\*\* - indicate significance at the 5, 1 and 0.1% level, respectively, n.s. – not significant differences

**Table 2.** Statistical significance of differences between DHA and ODR described by correlation

**(cm) ODR** 



> Soil organic matter (OM) has important effects not only on soil enzymes activities but first of all on microorganisms activities. Soil OM has been considered as an indicator of soil quality (similarly like dehydrogenases,) because of its character of nutrient sink and source that can enhance soil physical and chemical properties, and also promote biological activity (Salazar et al., 2011). Interestingly, not only amount of OM in the soil is important but most of all its quality, as OM affects the supply of energy for microbial growth and enzyme production (Fontaine et al., 2003).

> It is evident that soil enzymatic activity is strongly connected with soil OM content. The higher OM level can provide enough substrate to support higher microbial biomass, hence higher enzyme production (Yuan & Yue, 2012). Several authors reported positive correlation between DHA and OM content (Chodak & Niklińska, 2010; Moeskops et al., 2010; Romero et al., 2010; Zhao et al., 2010; Yuan & Yue, 2012).

> Zhang et al. (2010) indicated also that as well DHA and CaCO3 correlated with OM content, and what is more DHA, OM and CaCO3 were correlated with each other in their spatial distribution, suggesting that abundant OM content contributed to the formation of pedogenic calcium carbonate.

> Salazar et al. (2011) hypothesized that activities of dehydrogenases in different forest ecosystems are involved in the carbon cycling, and they also reported their positive relationships. Dehydrogenases, are highly associated with microbial biomass (MB), which in turn affects on decomposition of OM and the release of CaCO3 (Zhang et al., 2010).

> We also investigated effect posed by total organic carbon (TOC) and response of DHA in the agricultural used *Mollic Gleysol*, taken from Kosiorów village (SE part of Poland). We

determined significant (*P*<0.0001) correlation between TOC-DHA (Fig. 5). Mentioned strong relationship was also confirmed by high value of correlation coefficient (r=0.99\*\*\*). In our laboratory conditions the optimal value of TOC content for reaching maximal values of soil DHA was its level above 25%.

Dehydrogenase Activity in the Soil Environment 191

The literature data, currently available, referring to the connections between DHA and soil

Generally, enzyme activities tend to increase with soil pH (Błońska, 2010; Moeskops et al., 2010) – please put a space before Moeskops. Błońska (2010) determined significant positive

Fernandez-Calviño et al. (2010) noted significantly positive correlations among soil DHA and pH in the range of 4.1 (pHKCl) and 4.9 (pHwater), suggesting that acidity suppressed

Adequately, a study by Levyk et al. (2007) demonstrated that acidic conditions in the pH range between 1.5–4.5 resulted with strong DHA inhibition in relation to alkaline soils, whereas Ghaly & Mahmoud (2006) noted that under acidic conditions with pH less than 6.5,

According to Frankenberger & Johanson (1982), the weakening of enzymatic activity in soil with the increase of soil acidity is the effect of destroying ion and hydrogen bonds in

On the other hand, study performed by Włodarczyk et al. (2002) indicated maximum DHA at pH 7.1, similarly to the work of Ros et al. (2003), where optimum for DHA was noted for pH 7.6-7.8. Also Brzezińska et al. (2001) reported that the best pH conditions for DHA

Natywa & Selwet (2011) noted positive correlation between DHA and pH in soils under

Trevors (1984) concluded that very little DHA is observed below pH 6.6. and above pH 9.5. According to Nagatsuka & Furosaka (1980) the optimum range for DHA is contained between 7.4–8.5. However we should realize that many heterogeneous soil types might not

Our investigations, performed on *Mollic Gleysol* sample (from Kosiorów village) indicated however, that DHA also reached high level at lower pH values–between 5.5-5.73 (Fig. 6). Significant inhibition of DHA (even by 95%) we scarcely noted when soil pH was above

It is often assumed that pH may affects soil enzymes level in three different ways (Shuler &

1. by changing in the ionic form of the active sites of the enzymes, which consequently

Thus, the pH factor is considered to be the best predictor of DHA in the soil environment

correlation (r=0.50\*\*\*) DHA-pH(water) in the pH range 3.67-5.88.

the rate of TTC - specific substrate for DHA, did not decrease.

affect the enzyme activity and hence the reaction rate, 2. by altering the three-dimensional shape of enzyme, and 3. by affecting the affinity of the substrate to the enzyme.

(Quilchano & Marañon, 2002; Moeskops et al., 2010).

**3.4. pH** 

pH are still ambiguous.

potential enzyme activity.

enzyme active centre.

ranged between 6.6-7.2.

5.75.

Kargi, 2010):

maize growth at pH range from 5.17 to 7.27.

be included in mentioned above range.

**Figure 5.** Relationship between DHA and TOC content in the *Mollic Gleysol* (n=9, r=0.99\*\*\*), according to Wolińska & Stępniewska (unpublished data)

Analogically to our investigations also Koper et al. (2008) found and reported strong significant relationships between DHA and organic carbon content in *Haplic Podzol* soil samples, and they described mentioned correlations by r coefficient ranged between 0.56\* and 0.98\*.

The study of Kumar et al. (1992) indicated that DHA displayed the close, positive correlations not only with OM content but also with fungal population abundance in four forest stands (two at low and two at higher attitudes).

High correlation coefficient reported for enzymatic activities and TOC level suggested an important role of these enzymes in transformations of basic components of soil OM (Wolińska & Stępniewska, 2011). There is in general agreement with previous results indicated by Pascual et al. (2000), who found that soils characterized with low microbial and biological activity (e.g. low microbial carbon and low respiration rate), also display the lowest values of DHA.

Summarizing, the higher content of OM, the more active the soil microorganisms. Microorganisms accelerate the degradation of OM, which is reflected in soil respiration and release of carbon dioxide from the rizosphere (Zhang et al., 2010), thus DHA is positively correlated with OM content. Similarly, increase of DHA with higher microorganisms number was reported (Fontaine et al., 2003).
