Selenium toxicity in plants and its detoxication by phosphorus

Selenium toxicity and the effect of P application on Se in wheat (Triticum aestivum) was studied in a greenhouse experiment using the sandy soil of Haryana Agricultural University, Hissar, India. Selenium was applied at 0, 2.5, 5, and 10 ppm as Na2SeO3–5H2O, and P at 0, 50, and 100 ppm as KH2PO4. The application of P at 50 ppm increased, and that at 100 ppm decreased, dry matter, grain yield, N, S, Zn, Cu, chlorophyll, DNA, RNA, protein, and proline contents, and S-amino acids in wheat. Contents of Fe and Mn decreased as P increased to 50 and 100 ppm. Plant P increased with increases in added P up to 100 ppm. In P control and 50 ppm P treatments, the addition of Se decreased dry matter yield, grain yield, N, Zn, Cu at 50 days and maturity (135 days), DNA, RNA, protein, and proline in plants at 45 and 90 days after planting, and S-amino acids in grains, but 2.5 ppm Se with 50 ppm P increased, P, S, Fe, and Mn, and 2.5 and 5 ppm Se with 100 ppm P were beneficial on almost all parameters. Se content increased with 50 ppm P and all concentrations of Se, but decreased with 100 ppm P. Free amino acids were greater at 90 days than at 45 days sampling. Phosphorus application decreased free amino acids, but Se increased them.Sunflower (Helianthus annuus) was grown after wheat to see the residual effect of Se and P. In sunflower there was low accumulation of Se, which increased with high Se and 50 ppm P, and decreased with 100 ppm P applied to the wheat crop. But, in this case, 50 and 100 ppm P added to the wheat crop increased N, P, and S. At 100 ppm P added to wheat, 2.5 and 5 ppm Se showed increased dry matter, P, and S content at 90 and 135 days.The high amounts (2.5 ppm and above) of added and residual Se in soil decreased the growth of wheat and sunflower, the absorption of Zn, Cu, Fe, Mn, S, and N, and the synthesis of nucleic acids, chlorophyll, and protein, whereas P decreased the harmful effect of Se, and increased all the above parameters.