The Influence of Phosphorus on Arsenic Uptake/Efflux and As Toxicity to Wheat Roots in Comparison with Sulfur and Silicon

Hydroponic cultures were conducted to investigate the effects of phosphorus (P), sulfur (S), and silicon (Si) on arsenic (As) accumulation and toxicity to wheat seedlings. The results showed that As concentrations in roots and shoots of wheat seedlings and arsenite [As(III)] in the nutrient solution were significantly decreased with increasing P concentrations. Si had no significant effect on As accumulation in wheat seedlings until the Si concentration was increased to 960 A mu mol L-1. In the treatment with 960 A mu mol L-1 Si, both arsenate [As(V)] uptake and As(III) efflux were significantly decreased compared to the treatment without Si. The application of 480 and 960 A mu mol L-1 S resulted in a significant decrease in As concentrations in wheat shoots, but an increase in As accumulation in wheat roots. Both total As(III) efflux and the relative As(III) efflux were significantly decreased when the S concentration was 960 A mu mol L-1. Different concentrations of P significantly increased the relative root elongation (RRE), total root length (TRL), root surface area (RSA), root volume (RV), and number of root tips (NRT), and decreased root average diameters (RAD). There were no significant effects of S on RRE, TRL, RSA, RV, RAD, and NRT of wheat seedlings under 15 A mu mol L-1 As(V). Silicon with concentration of 960 A mu mol L-1 significantly increased TRL and TRS of wheat seedlings when compared with the treatment without Si under 15 A mu mol L-1 As(V).