Effect of Different Zn~(2+) Activities on Nutrient Absorption of Rice ( Oryza sativa L.)and Their Genotypes Difference in Zn Nutrient

The genotype difference and effect of different Zn 2+ activities on rice nutrient absorption were studied with the Zn efficient cultivars IR34, IR36, IR8192 and Zn inefficient cultivars IR26, Erjiufeng , Ce64 7 grown in chelate buffered nutrient solution at Zn supplies range from deficient to sufficient (free Zn activities from 0 μm to 40 μm, pZn from11.5 to 9.7). The results showed that: the critical Zn 2+ activity is much more different for Zn efficient rice genotypes and Zn inefficient. It is higher for Zn inefficient rice genotypes, pZn 2+ 10.3 for IR26, pZn 2+ 10.3~10.6 for Ce64 7 , and lower for Zn efficient, pZn 2+ 10.6~11.0 for IR34 and IR8192, respectively. Therefore, pZn 2+ 10.6~11.0 might be an effective Zn 2+ activity to identify Zn efficient rice genotypes. The critical Zn content of Zn inefficient rice shoots higher than of Zn efficient rice shoots. In this study, the critical Zn of shoot at 7 leaf old seedlings was, more than 24.52 mg/kg for IR26, 18.32~23.81 mg/kg for Ce64 7, 18.32~18.52 mg/kg for IR34 and 14.65~15.34 mg/kg for IR8192. When Zn 2+ activity decreased, Zinc and phosphorus quantity absorbed by rice plant decreased, but zinc and phosphorus translocation rate from root to shoot increased and nutrients ratio of Fe/Zn, Cu/Zn, P/Zn were enhanced. At lower Zn 2+ activities, the shoot zinc content was less decreased in Zn efficient rice genotypes than that in Zn inefficient rice genotypes. But Zn efficient rice genotypes have lower Zn requirement and ability to maintain lower Cu/Zn , P/Zn ratio in the shoot than Zn inefficient rice genotypes. Therefore, at zinc deficit condition, the mechanism of resistance to zinc deficit for Zn efficient rice genotypes is that they have lower Zn requirement, more efficient Zn translocation from root to shoot and ability to limit translocation of Cu, P from root to shoot to keep the stability of nutrient ratio.