Differential response of barley varieties to Fe stress

Previous studies indicated that plant genotypes which tolerate acid soils may be susceptible to Fe stress when grown at high pH. Evidence of this relationship was obtained through comparisons of species adapted to strongly acid or alkaline soil environments and of plant populations within species which differ widely in acid or alkaline soil tolerance. Such a correlation between Fe inefficiency and tolerance to excess Al has not been shown for barley (Hordeum vulgare L.). The purpose of the present investigation was to determine whether barley varieties, representing a range of Al tolerance, also respond differently to Fe stress. Al‐tolerant ‘Dayton’ and Al‐sensitive ‘Kearney’ barley were grown in nutrient solutions containing Fe concentrations ranging from 0.025 to 2.0 ppm, as FeEDDHA, at an initial pH of 6.5. Kearney was more resistant to Fe deficiency than Dayton and maintained more normal growth at the lower Fe levels. In addition, this variety established a lower pH in the root zone and a higher rate of NH+ 4‐N uptake at all concentrations of Fe. The greater susceptibility of Dayton to Fe stress was characterized by leaf chlorosis, reduced top growth and a greater accumulation of Ca, Mn, and P in the tops of plants subjected to Fe treatments below 0.5 ppm. Although the specific mechanisms for plant resistance to Fe stress were not determined, it is apparent that the maintenance of a low pH in the root zone, effective uptake of NH+ 4‐N and efficiency in the absorption and transport of Fe, while preventing excess uptake of other essential elements constitute an advantageous response to Fe stress.