We studied the influence of a weak, extremely-low-frequency magnetic field (MF) with a frequency of 50 Hz and a peak amplitude of  103 µT and aluminium solution (in the form of AlCl3) at different concentrations (0, 40, 70, 100, 130, 160, 400, 800, 2000 and 5000 µM) on the growth of spruce seedlings  (Picea abies). The results showed that stimulatory and statistically significant MF effects on the growth of seedlings were observed only with 100 µM aluminium solution. Slight stimulative effects were also observed within the range of concentrations between 40 and 160 µM Al3+ (all the stimulated groups taken together). Germination and fresh weight were not significantly influenced. At these concentrations the aluminium solution alone (without MF) or the MF alone (without Al3+) did not influence the growth parameters.
These results suggests the importance of synergistic action of the MF with environmental factors as well as the existence of 'physiological windows' beside the frequency and power ones.