The effect of Cd, Cu, Pb, and Zn on denitrification of three Pseudomonas species in a liquid culture medium (Giltay) and in autoclaved soil, as well as on the denitrifying activity of native soil, was investigated. In Giltay medium, Cd in concentrations starting at 50 µg/ml strongly inhibited growth and denitrification of an unidentified Pseudomonas sp., P. aeruginosa, and P. denitrificans, while Zn and Pb did not influence the denitrifying activity even up to 500 µg/ml. Cu at 50 µg/ml inhibited denitrification of P. aeruginosa and the unidentified Pseudomonas sp.; however, it had no influence on P. denitrificans. When the three bacteria were inoculated into autoclaved soil their reaction to Cd and Cu was similar to that in Giltay medium, but the accumulation of nitrite was considerably higher. Zn, which showed no effect in the liquid medium at 500 µg/ml, inhibited the denitrifying activity of all bacteria in the soil at this concentration. Denitrification in native (nonautoclaved) soil was also inhibited by the addition of increasing amounts of heavy metals. This was indicated by an accumulation of nitrite and nitrous oxide which appeared to a lesser degree and for a shorter time period in nontreated samples.

Tested soils (1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002) were defined by chemical, textural and microbial characteristics. From the tests which describe cambisols, the following parameters have to be stressed. The higher level of C org (1.20-1.76%), which resulted in quite high microbial biomass carbon content (396-625 µg/g dry soil), high control respiration (0.45-0.80 mg CO 2 /h/ 100 g dry soil) and potential nitrification with (NH 4 ) 2 SO 4 (6.7-18.4 mg N-NO 3 /8 days/100 g dry soil). Studied luvisols reached typical levels: C org (0.97-1.22%), C MB (398-503 µg/g dry soil), control respiration (0.46-0.57 mg CO 2 /h/100 g dry soil), potential nitrification with (NH 4 ) 2 SO 4 (3.2-9.9 mg N-NO 3 /8 days/100 g dry soil). Lower levels of organic carbon and a medium level of microbial biomass raised in higher ratio C MB /C org (average 4.0%). Highly significant differences (p < 0.01) between cambisols and luvisols were determined for C org , N t , pH(KCl), C MB , C MB /C org , C E , control respiration and potential nitrification, while the difference in potential ammonification with peptone was at level p < 0.05. With the exemption of ratio C MB /C org all cambisol characteristics were higher than luvisol ones. Studied soils were evaluated by six biological criteria (C MB ; ratios: C MB /C org , C E /C MB , potential/control respiration, potential/ control ammonification, potential/control nitrification). These criteria distinguished tested soils into three groups. The first one includes two localities in the mountain region (Červená Voda 809, 810; altitude 565-590 m) defined as stagnic cambisols with higher content of C org (1.40, respective 1.76%) and simultaneously with the highest biomass of micro-organisms from all tested soils (C MB , 625, respective 621 µg/g dry soil). It is not surprising that microbial activities (respiration, nitrification) at these localities were also high. The majority of the studied localities (one eutric cambisol and four luvisols) belongs to the medium group. The third group includes two localities (Neumětely -haplic luvisol, Čistá u Rakovníka -eutric cambisol) where biological criteria was mostly the worst. In the period 1993-2002 microbial biomass carbon was for both sites in the range of 357-458 µg/g dry soil which are not so bad values, but in comparison with localities in mountain wet region they are low. This status was issued in the lower ratio C MB /C org (2.71-3.77%).

for their valuable help, critical remarks and comments.

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Microbial biomass-C [MBC] (1) arable Cambisols (100%), (2) cut and grazed grasslands (547%), (3) forest mineral horizon A H : 0-50 mm (783%) and (4) Norway spruce forest floor (2421%). The ratio EC-Ca/EC-K reached on average 62% and ranged from 48% to 74%. Correlation between EC-K and EC-Ca values is connected with soil organic ma�er status; the correlation was very close for Cambisols (r 2 = 0.925), a medium correlation was found for forest floor (r 2 = 0.380) and a weak correlation was observed for Podzols (r 2 = 0.042). The correlation between MBC-K and MBC-Ca was very close in all cases: Cambisols (r 2 = 0.811), Podzols (r 2 = 0.904) and forest floor (r 2 = 0.496). The ratio between organic carbon and organic nitrogen in 0.01 mol/l CaCl 2 extracts [EC-Ca/N org ] could be declared as a new indicator for soil microbial association status.