Graduate Thesis Or Dissertation
 

A new hypothesis to explain phosphorus-induced zinc deficiencies

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  • The phenomena known as "phosphorus-induced zinc deficiencies" are poorly understood. Conclusions drawn from research efforts designed to identify the mechanism of the phosphorus-zinc interaction are, in many cases, incompatible. Similarities in the data from a number of literature reports of "phosphorus-induced zinc deficiencies" have led to the development of the hypothesis that so-called "phosphorus-induced zinc deficiencies" result from the correction of phosphorus deficiencies in growth mediums which are also potentially zinc deficient. To test this hypothesis, corn, beans, and potatoes were grown in dithizone purified nutrient solutions consisting of three zinc levels (0, .1356, and .4068 μM Zn²⁺) in factorial combination with four phosphorus levels (.02, .10, 1.0, and 3.0 mM PO₄³⁺). Yield, and the concentration and uptake of zinc, phosphorus, iron, manganese, potassium, calcium, magnesium, and sulfur were measured for the roots, stems, and leaves for each plant species. Deficiency symptoms and yield responses to phosphorus and zinc were in agreement with the above stated hypothesis in that zinc deficiencies and yield responses to zinc were obtained for all three plant species only after phosphorus deficiencies were corrected. In no case did increasing phosphorus level in the nutrient solution induce a zinc deficiency when zinc was at a low, but adequate, level in the nutrient solution. Reductions in zinc concentration in plant tissue with increasing phosphorus concentration in the nutrient solution could be explained as dilution effects, and in no case was total zinc uptake reduced by increasing the concentration of phosphorus in the nutrient solution. Although reductions in the top to root zinc concentration ratio were observed as phosphorus level in the nutrient solution was increased, the apparent reduction in zinc translocation can be explained on the basis of dilution of plant zinc by the yield response to phosphorus. Evidence is presented to indicate that high phosphorus levels in plant tissue do not induce a zinc deficiency, but rather are the result of zinc deficiency under conditions of high phosphorus availability. The hypothesis presented in this investigation also adequately explains a much greater proportion of the data in the literature on "phosphorus-induced zinc deficiencies" than do other hypotheses. In contrast to other hypotheses, the hypothesis presented in this investigation also adequately explains the data from those reports in the literature in which high rates of phosphorus were applied without inducing a zinc deficiency. It is suggested that the use of the misleading description, "phosphorus-induced zinc deficiency," be discontinued and that the phenomena be described as what they really are: zinc deficiencies resulting after the correction of phosphorus deficiencies on growth mediums which are also potentially zinc deficient.
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file details ChristensenNeilW1972.pdf 2017-08-23 Público Baixar