Potential for Phosphorus Toxicity in Zinc-Stressed Corn and Potato

To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. The published article is copyrighted by Soil Science Society of AmericaCorn (Zea mays L., 'Illinois WF 9x38-11') and potato (Solanum\ud tuberosum L., 'Russet Burbank') were grown in dithizone purified\ud nutrient solutions to contrast relationships between dry matter yield,\ud tissue phosphorus (P) concentration, and tissue zinc (Zn) concentration\ud as they influence the development of Zn deficiency and P toxicity.\ud Treatments consisted of Zn at 0, 0.14, and 0.41 μM in factorial combination\ud with P at 0.02, 0.10, 1.0, and 3.0 mM. Yield and tissue concentration\ud of P and Zn were affected by statistically significant P-Zn\ud treatment interactions in both species. Corn plants developed Zn deficiency\ud symptoms and responded to nutrient solution Zn when plant\ud growth was not limited by inadequate nutrient solution P. Corn plants\ud grown in nutrient solutions containing 0 μM Zn and 3.0 mM P contained 3.39% P in leaf tissue and had significantly lower yields than\ud did plants grown in nutrient solutions containing 1.0 mM P. Even\ud though no visual symptoms were evident, P toxicity probably was\ud responsible for the reduction in yield. Potato plants responded to\ud nutrient solution Zn when growth was not limited by inadequate P but\ud did not exhibit visual symptoms of Zn deficiency. Zinc--deficient\ud potato plants containing in excess of 2.22l% P in leaf tissue exhibited\ud probable P toxicity symptoms characterized by puckering of leaf\ud edges, thickening and upward curling of leaves, and leaf necrosis. Excessive concentration of P in leaf tissue of Zn-deficient potato was the\ud result of increased mobilization and translocation of P from roots to\ud above-ground parts, increased total P uptake, and concentration of P\ud resulting from restricted growth. Excessive levels of P in corn leaf\ud tissue were primarily the result of concentration of P due to restricted\ud growth. Zinc concentration in tissue of both species was reduced by\ud growth response dilution, but Zn uptake by plants receiving low levels\ud of Zn was not reduced by increasing nutrient solution P concentrations.\ud Apparent accentuation of Zn deficiency by P application is explained\ud on the basis of accumulation of toxic levels of P in Zn-\ud deficient plants. Species such as potato which show increased P uptake and increased mobilization and translocation of P to tops when\ud under Zn stress are probably more susceptible to P toxicity