Influence of phosphorus limitations on the growth,nutrient partitioning and physiology of mahogany (Swietenia macrophylla King) seedlings

The effects of four rates of phosphorus (P) fertilization (0, 0.56, 5.6 and 56.0 mg l^?1) in soilless medium on the growth and physiology of mahogany seedlings were examined. The greatest response occurred at the 56 mg l^?1 rate, with relatively small differences between other treatments. Biometric parameters increased at the 56 mg l^?1 compared to 0 mg l^?1 rate except root dry mass. Both the concentration and the total content of P and Kjeldahl nitrogen (N) increased in leaves, stems and roots with P application rate. Foliar concentrations of potassium (K), calcium (Ca), magnesium (Mg), manganese (Mn) and sulfur (S) declined, and boron (B) and copper (Cu) increased with P limitations; zinc (Zn) and iron (Fe) were unaffected. Physiological adaptations of mahogany to P limitations include the preferential allocation of carbon (C) to plant roots, and increases in P utilization efficiency, P acquisition efficiency and the concentration of organic acids in xylem fluid. Root phosphatase activity was not influenced by P fertilization.