Ecotypes of Holcus Lanatus Tolerant to Zinc Toxicity also Tolerate Zinc Deficiency

Genotypes tolerant to zinc (Zn) toxicity, if they accumulate Zn in their roots, may grow better than Zn-sensitive genotypes, even in Zn-deficient soil. In the present study, Holcus lanatus L. ecotypes differing in tolerance to Zn toxicity were grown in Zn-deficient Laffer soil which was amended with Zn to create a range of conditions from Zn deficiency to Zn toxicity. Increasing Zn additions to the soil, up to the sufficiency level, improved growth of all ecotypes. At toxic levels of added Zn, the Zn-sensitive ecotype suffered a greater decrease in growth than the Zn-tolerant ecotypes. All ecotypes accumulated more Zn in roots than in shoots, with root concentrations exceeding 8 g Zn kg(-1) dry weight in extreme cases. When grown in Zn-deficient or Zn-sufficient soil (up to 0.5 mg Zn kg(-1) soil added), ecotypes tolerant to Zn toxicity took up more Zn, grew better and had greater root and shoot Zn concentration than the control (Zn-sensitive ecotype). Zn-tolerant ecotypes transported more Zn, copper (Cu) and iron (Fe) from roots to shoots in comparison with the Zn-sensitive ecotype. The average Zn uptake rate from Zn-deficient soil (no Zn added) was greater in the Zn-tolerant ecotypes than in the Zn-sensitive ecotype. In conclusion, ecotypes of H. lanatus that are tolerant to Zn toxicity also tolerate Zn deficiency better than the Zn sensitive ecotype because of their greater capacity for taking up Zn from Zn-deficient soil. This is the first report of the coexistence of traits for tolerance to Zn toxicity and Zn deficiency in a single plant genotype. (C) 2000 Annals of Botany Company.