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    Florida Agricultural Experiment Stations Journals Series No. 1691.

  • † Present address: Associate Professor, University of Florida, IFAS, AREC, P.O. Box 1088, Lake Alfred, FL 33850.


In an initial experiment, inoculation of sour orange (Citrus aurantium L.) seedlings in sand with Glomus fasciculatus greatly increased growth with or without fertilization with P or Cu. Application of P or Cu to non-mycorrhizal seedlings in sand did not stimulate growth. Application of P to non-mycorrhizal seedlings in a sandy loam soil increased growth, but induced Cu deficiency symptoms and reduced foliar Cu concentrations. Application of P to mycorrhizal seedlings did not induce Cu deficiency symptoms, but reduced foliar Cu concentrations slightly. In a complete factorial experiment, sour orange seedlings in the sandy loam soil, were inoculated with G. fasciculatus or not inoculated, fertilized with 5 levels of P from 0 to 800 mg P 1-1 of soil and 3 levels of Cu from 0 to 8.6 mg 1-1. Non-mycorrhizal seedlings, which received no Cu, developed copper deficiency symptoms which were most severe at 200 mg P 1-1. Copper deficiency symptoms did not appear on the seedlings receiving no P because seedlings failed to grow. Deficiency symptoms disappeared and foliar Cu concentrations increased when seedlings were fertilized with P at 800 mg 1-1 probably because the high rates of P decreased the pH making Cu more soluble. On seedlings inoculated with G. fasciculatus and not fertilized with Cu, increasing rates of P decreased percentage mycorrhizal infection, the number of chlamydospores per g of soil, and the foliar Cu concentrations. Copper deficiency symptoms occurred only at 800 mg P 1-1 and were mild. No Cu deficiency symptoms occurred and foliar Cu concentrations were in the optimum range where Cu was applied. Apparently, P induces Cu deficiency by stimulating growth of non-mycorrhizal seedlings until Cu becomes the limiting nutrient, whereas, P-induced Cu deficiency appears to be due to P inhibition of mycorrhizal development on seedlings inoculated with G. fasciculatus.