Abstract: By using hydroponics, this paper studied the physiological responses of trifoliate orange (Poncirus trifoliata)seedlings to the deficiency of zinc (0 μmol·L^-1Zn²⁺) and/or iron (0 μmol·L^-1Fe-EDTA). The deficiency of both Zn and Fe decreased the plant biomass and root viability, and increased the leaf-and root SOD activity significantly. Zinc deficiency increased the leaf-and root POD significantly, while Fe deficiency had an adverse effect. The root CAT activity increased significantly under Zn deficiency, but had less difference with the control under Fe deficiency. Fe and Zn deficiency induced a significant decrease of root potassium (K), magnesium (Mg), and phosphorus (P) contents and of shoot K content, respectively, but resulted in a significant increase in the root-and shoot Zn and Cu contents and in the root Fe and Mn contents and shoot Mn content, respectively. Ultrastructural observation of leaf structure and chloroplast showed that under Fe deficiency, the organelle was damaged seriously, which was revealed by the vacuolization of chloroplast and mitochondria, vague chloroplast membrane and thylakoid lamella, drastic increase of platoglobuli number, and absence of starch grain in the chloroplast. Under Zn deficiency, the thylakoid lamella of chloroplast was loosely distributed with less lamella, but the platoglobuli number was increased.

Key words: zinc, iron, Poncirus trifoliata, physiological index, mineral content, ultrastructure, moving sand dune, species distribution pattern, interspecific correlation, allometric growth.