Effect of P/As molar ratio in soil porewater on competitive uptake of As and P in As sensitive and tolerant rice genotypes.

Phosphorus (P) can affect the bioavailability and mobility of arsenic (As) in paddy soil-plant system, but it is not clear how different forms of phosphorus fertilizers affect P/As molar ratio in soil and how the ratio in turn affects the competitive uptake of P and As in two genotypes. Different P fertilizers, i.e., calcium-magnesium phosphate (CMP), superphosphate (SP) and potassium phosphate monobasic (PPM), were used to investigate the difference in competitive uptake between As sensitive (IIY3301) and As tolerant (SY9519) rice genotypes. Our results indicated that the contents of total As in brown rice of PPM and SP treatments (II-PPM and II-SP) were 15.4% and 26.9% lower than that of CMP treatment (II-CMP) for IIY3301 genotype, but their P contents were 27.0% and 17.8% higher than that of II-CMP treatment. However, the As content in brown rice showed no significant difference between PPM and CMP treatments for SY9519 genotype (S-PPM and S-CMP). The net As accumulation in shoots of II-PPM during the tillering stage was significantly lower than that of II-CMP, but the difference of net As accumulation between S-PPM and S-CMP was not significant. The As translocation factor in II-PPM and II-SP were 16.7% and 22.2% lower than that in II-CMP, but the difference of As translocation factor between S-PPM and S-CMP was not significant. In addition, the contents of total As in porewater showed no significant difference between PPM and CMP. Conversely, the P/As molar ratio in porewater of PPM during tillering stage was 10.9% higher than that of CMP. In summary, PPM led to a higher P/As molar ratio in porewater, which promoted the competitive uptake of As and P by IIY3301 genotype; and the competitive uptake of As and P was more likely to occur in As sensitive rice genotype than in As tolerant rice genotype.