As other mine tailings (Ye et al., 2002), the four sites had low nutrient contents, combined with high concentrations of pseudo-total and CaCl
extractable metals (Table 1). CaCl-extractable metal concentration usually well predicts the metal fraction readily available to microorganisms and plants, i.e. metal bioavailability (Peijnenburg and Jager, 2003). Our mine soil was deficient in essential plant macronutrients (N, P, and K), which might explain the low vegetation cover and limited plant growth in many zones of the mine. In any event, soils from vegetated sites presented higher values of OM, oxidable OM, and total N, compared with non-vegetated soils (Table 1).
Pseudo-total and CaCl
-extractable Pb and Zn concentrations widely varied across these four sites (Table 1). For all ones, pseudo-total Pb and Zn concentrations greatly surpassed the Reference Critical Values reported for ecosystems protection in the Basque Country (330 and 840 mg kg for Pb and Zn, respectively) (IHOBE, 1998). As expected,
values of CaCl
-extractable metal concentration were much higher for Zn than for Pb. Site V2 had the highest CaCl
2
-extractable Zn concentration, followed by V1, NV1 and NV2. The highest CaCl
2
-extractable Pb concentrations occurred for NV1 and V2. Many soil physicochemical properties can affect metal sorption in soil. In this respect, NV2 presented significant higher soil pH values, compared to all the other sites. This can explain the lower CaCl
2
2
-extractable Pb and Zn values in the non-vegetated NV2 soil, as also reflected in lower Kd (distribution coefficient) values. Immediately before amendment application (0 month), values of microbial parameters (basal respiration, SIR, and OEA) were generally higher in vegetated than non-vegetated sites (p b 0.05) (Figs. 1 and 2, Table S2). The lack of vegetation together with concomitant low soil OM content usually have an adverse effect on soil microbial biomass and activity. In contrast, the plant community can enhance microbial properties of metalcontaminated mine soil (Hernández-Allica et al., 2006). In general, at 0 month, lower or similar values of microbial parameters were found in the NV1 soil than in the NV2 one (p b 0.05): these lower values may reflect significant higher values of CaCl
-extractable Pb in the NV1 soil (Table 1). Vegetated soils (V1 and V2) had higher CaCl
2
2
-extractable Zn values than non-vegetated soils (NV1 and NV2): in vegetated soils, Zn was probably sorbed to roots (Table 1), while, in non-vegetated soils, labile Zn might have been lost through leaching. The beneficial effect of vegetation on soil microbial communities more than counteracts the potential negative effect of higher bioavailable Zn concentrations. By contrast, at 0 month, soil phytotoxicity, as reflected by L. sativa root elongation, was in many cases not significantly different in vegetated versus non-vegetated sites (Fig. 3).As other mine tailings (Ye et al., 2002), the four sites had low nutrient contents, combined with high concentrations of pseudo-total and CaClextractable metals (Table 1). CaCl-extractable metal concentration usually well predicts the metal fraction readily available to microorganisms and plants, i.e. metal bioavailability (Peijnenburg and Jager, 2003). Our mine soil was deficient in essential plant macronutrients (N, P, and K), which might explain the low vegetation cover and limited plant growth in many zones of the mine. In any event, soils from vegetated sites presented higher values of OM, oxidable OM, and total N, compared with non-vegetated soils (Table 1).Pseudo-total and CaCl-extractable Pb and Zn concentrations widely varied across these four sites (Table 1). For all ones, pseudo-total Pb and Zn concentrations greatly surpassed the Reference Critical Values reported for ecosystems protection in the Basque Country (330 and 840 mg kg for Pb and Zn, respectively) (IHOBE, 1998). As expected,values of CaCl-extractable metal concentration were much higher for Zn than for Pb. Site V2 had the highest CaCl2-extractable Zn concentration, followed by V1, NV1 and NV2. The highest CaCl2-extractable Pb concentrations occurred for NV1 and V2. Many soil physicochemical properties can affect metal sorption in soil. In this respect, NV2 presented significant higher soil pH values, compared to all the other sites. This can explain the lower CaCl2
2
-extractable Pb and Zn values in the non-vegetated NV2 soil, as also reflected in lower Kd (distribution coefficient) values. Immediately before amendment application (0 month), values of microbial parameters (basal respiration, SIR, and OEA) were generally higher in vegetated than non-vegetated sites (p b 0.05) (Figs. 1 and 2, Table S2). The lack of vegetation together with concomitant low soil OM content usually have an adverse effect on soil microbial biomass and activity. In contrast, the plant community can enhance microbial properties of metalcontaminated mine soil (Hernández-Allica et al., 2006). In general, at 0 month, lower or similar values of microbial parameters were found in the NV1 soil than in the NV2 one (p b 0.05): these lower values may reflect significant higher values of CaCl
-extractable Pb in the NV1 soil (Table 1). Vegetated soils (V1 and V2) had higher CaCl
2
2
-extractable Zn values than non-vegetated soils (NV1 and NV2): in vegetated soils, Zn was probably sorbed to roots (Table 1), while, in non-vegetated soils, labile Zn might have been lost through leaching. The beneficial effect of vegetation on soil microbial communities more than counteracts the potential negative effect of higher bioavailable Zn concentrations. By contrast, at 0 month, soil phytotoxicity, as reflected by L. sativa root elongation, was in many cases not significantly different in vegetated versus non-vegetated sites (Fig. 3).
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