## 3 Results and Discussion
### Effect of Adaptation to Cd Stress on Biomass of the Middle European Ecotype of S. nigrum
Pot experiments on the Korean ecotype _S. nigrum_ L. from Daegu (35\({}^{\circ}\)88\({}^{\prime}\) N, 128\({}^{\circ}\)59\({}^{\prime}\) E) cultivated in a growth chamber at 25 \({}^{\circ}\)C, 14 h photoperiod and 60% relative humidity in sand soaked with half-strength Hoagland nutrient solution, also indicated a decrease of biomass (DW) of leaves, stems and roots by 79, 75.6, and 75%, respectively, at exposure of plants to 50-80 mg kg\({}^{-1}\) Cd [36]. The Korean ecotype grown in untreated medium, at shoot biomass comparable to Chinese and Japanese ecotypes, and about two-fold bigger root biomass, displayed its very sharp decline in the treatment range from 10 to 50 mg kg\({}^{-1}\) Cd, but no significant changes at further increase of Cd concentrations to 80 mg kg\({}^{-1}\). This indicates the launch of a new defense mechanism under the deep stress conditions. The sensitivity of plants to Cd in this experiment may have been additionally affected with the growth medium close to hydroponic conditions. This usually results in bigger Cd accumulation in plants, but in adequately higher stress than at Cd uptake by plants from soil. One more comparative pot experiment conducted at a glasshouse on the Australian (Melbourne) and Chinese (SY) ecotypes grown in burozem soil from the La Trobe University campus (Melbourne) at 20 \(\pm\) 5 \({}^{\circ}\)C and natural light, showed about 30% lower biomass of the Ausralian ecotype, and similar tolerance to Cd content in the soil [16]. Concentration of 20 mg\({}^{-1}\) kg Cd in the soil was a threshold content assuring plant resilience. A sharp decline of biomass by 85-90% at 40 mg\({}^{-1}\) kg Cd and no further significant changes up to 80 mg\({}^{-1}\) kg Cd in the soil indicated similar reaction of studied Chinese (SY) and Australian _S. nigrum_ ecotypes to stress as it was observed with respect to Korean ecotype. It appears that under very high stress, new defense mechanisms start to act, however after a very serious damage to plant physiology. In contrast, such breakdown of defense mechanisms has not been observed in the Middle European ecotype of _S. nigrum_, in both non-adapted N0 and adapted A50 varieties. In these varieties, a decline in biomass occurred gradually and smoothly, and on a relatively small scale, in particular compared to Asian/Australian ecotypes. There is no other evidence of different, much weaker reactions of European ecotypes to Cd stress. However, a reported reduction in shoot biomass (DW) scarcely by 64% compared to control in the Provence (France) ecotype of _S. nigrum_ in the pot experiment at 100 mg\({}^{-1}\) kg Cd in the clayey loam soil [12] suggests considerably higher natural resistance of European ecotypes. Cd Accumulation, Enrichment and Translocation in the Natural (N0) and Adapted (A50) Plants Exposed to Growing Cd Stress  
Increasing contents of Cd in the soil resulted in growing concentrations of Cd in roots and shoots of the Middle European ecotype of _S. nigrum_, both of non-adapted (N0) and adapted to high concentrations of Cd (A50). However, Cd uptake by both varieties differed substantially. The non-adapted variety appeared to accumulate somewhat bigger contents of Cd in the root system over the entire range of Cd concentrations in the soil, evidently due to its lesser transport with xylem sap to shoots (Table 2). This manifested itself in noticeably bigger Cd concentrations, and even more visible accumulation of Cd loads in shoots of the adapted variety A50 within the entire range of elevated Cd concentrations in the soil (T10-T50).