THE RELATIONSHIP BETWEEN NICKEL TOXICITY AND IRON SUPPLY

The influence of varying levels of iron and substrate pH on the uptake of nickel and the intensity of toxicity symptoms in oat plants have been investigated using sand-and water-culture techniques.
Nickel-toxicity symptoms (both necrosis and chlorosis) are less severe when the concentration of iron in the nutrient solution is high. The reduction in degree of necrosis is related to a reduced content of nickel in the leaf blades, whilst that of chlorosis is related to the Ni/Fe ratio in the leaf blades—an internal antagonism being indicated in the latter case.
A reciprocal relationship exists between the nickel and iron contents of the leaf blades; the nickel content is materially reduced by high concentrations of iron in the nutrient solution, and the iron content by nickel, the former being the more pronounced effect.
Uptake of nickel increases with increasing pH for a constant iron level in the substrate, although the degree of necrotic symptoms is similar over pH range 4–7. Iron uptake is reduced by both nickel and increasing pH and results in chlorosis at pH values of 5·5 and above.
For a constant level of iron supply the phosphate content of the stem extracts is higher the greater the degree of nickel toxicity; the phosphorus status of the plant may be a factor in producing nickel toxicity but if so, it has to be considered in relation to other factors.