Phosphorus-Zinc Interaction and Iron and Manganese Uptake in the Growth and Nutrition of Phalaenopsis (Orchidaceae)

Visual symptoms of Zn deficiency, induced by excessive P applications, have been observed in commercial orchid nurseries. The supply of other metallic micronutrients, such as Fe and Mn, may also be inadequate in the plant due to high application rates of P. The aim of this study was to investigate this interaction in the nutrition of Phalaenopsis plants. Experimental treatments consisted of three P rates (0.0, 0.5, and 1.0 g L-1) and three Zn rates (0.00, 0.35, and 0.70 g L-1), as well as fertilization with other basic nutrients, and a control treatment with the fertilizer B&G Orchidée(r), at 1.0 g L-1. Dry matter production was evaluated, as well as the levels of P, Zn, Fe, and Mn in both shoots and roots. Higher P rates induced higher shoot dry matter production. However, symptoms of Zn deficiency were observed in plants treated with the highest P rate in the absence of Zn. With increasing P rates, Zn concentrations in the shoots decreased more markedly than in roots, with accumulation of the element in the roots, indicating low Zn translocation to the shoot. A much higher Mn content in shoots (661 mg kg-1) than in roots (75 mg kg-1) suggested that the species is highly tolerant to this micronutrient. The Fe concentrations in the plant were much higher than those indicated in the literature as critical levels for this genus.