The study aimed to find out the dynamic changes of selenium (Se) uptake with crops growing and to provide better understanding on the translocation of Se in soil-plant system. Pot experiments and laboratory analysis were carried out, in which 6 crops were planted for eight weeks in the soils treated with selenite and selenate. The results showed that there was a significant difference in the plant dynamic uptake pattern for selenite and selenate. Se concentration in shoots and roots of all tested plants continuously declined with growth since the third week after planting for selenate treatment; while Se concentration in roots of plants gradually increased with the growth, and that for shoots firstly increased and then leveled off or decreased for selenite treatment. Crops could accumulate Se throughout the whole growing period, while 80% of the Se in plants was uptaken in the first 6 weeks. Among the 6 tested plants, the Se concentration in the shoots and roots of mustard was the highest, followed by the shoots of wheat for selenate treatment. The Se concentration in shoots of carrot was the highest, while that in roots was the lowest for selenite treatment. For the same Se treatment, the Se concentrations in both roots and shoots of broccoli, purple cabbage and flowering Chinese cabbage were similar. Broccoli, purple cabbage, flowering Chinese cabbage, mustard and wheat had higher translocation ability to transport selenate than selenite from roots to shoots, whereas carrot had the same ability for translocating selenite and selenate. Biological dilution affected the dynamic changes of the Se content in crops, especially for selenate treatment, and a significant negative correlation between Se concentration of plants and their biomass further verified this. However, the changes of biomass of plants with growing period couldn't explain the total inverse dynamic uptake pattern for selenite and selenate. A significant positive correlation was observed between Se accumulations amount in six crops with available Se changes in soil during the corresponding growing period for selenate treatment, while no such correlation was found for selenite treatment. Se accumulation in crops grown on selenite-treated soil accounted for 0.5%-18.1% of soil available Se, whereas that in selenate treatment was 1.1-4.5 times of soil available Se except for carrot. In conclusion, the dynamic changes of Se uptake with crop growth were the comprehensive results of the absorption and transport capacity of crops, Se availability in soil and biological dilution. It should be considered as a whole in the selenium biofortification.
Keywords: available selenium; dynamic uptake; selenate; selenite; translocation.