Influence of thermal regime of soil on the sulfur (S) and selenium (Se) concentration in potato plants.

Three consecutive years of field experiments were carried out to investigate the effect of different root temperatures, induced by the application of mulches on the concentration of sulfur (S) forms (organic-S, total-S and SO4(2-)) and Se in different organs of potato plants (roots, tubers, stems and leaves). Four different plastic covers were used (T1: transparent polyethylene; T2: white polyethylene; T3: white and black coextruded polyethylene, and T4: black polyethylene), using uncovered soil as control (T0). The different treatments had a significant effect on mean root temperatures (T0 = 16 degrees C, T1 = 20 degrees C, T2 = 23 degrees C, T3 = 27 degrees C and T4 = 30 degrees C) and induced a significantly different response in the S forms and Se concentration, showing the T3 treatment (27 degrees C) the greatest concentration of total S and organic S in the stems and leaflets. The Se reached higher levels in the roots and tubers in T3. With regard to possibilities in phytoremediation, it is necessary to control the thermal regime of the soil to optimize the accumulation of elements.