Early growth in a congeneric pair of savanna and seasonal forest trees under different nitrogen and phosphorus availability

Most of the physiognomies of the Brazilian Cerrado fall within the definition of tropical savanna. However, patches of seasonal forest are interspersed within the Cerrado. The occurrence of savannas in areas whose climate allows forests may be related to the nutrient-poor soil, especially nitrogen (N) and phosphorus (P). We analysed the initial development of a congeneric pair, Handroanthus aureus, a savanna species, and H. impetiginosus, a seasonal forest species, to test whether these nutrients shape their functional traits differently. We used a hydroponic system with four treatments: (1) complete Hoagland solution containing N, P, K, Ca, Mg, S, O, H, Cl, B, Mn, Zn, Cu, Mo and Fe (2) Hoagland solution without P, (3) Hoagland solution without N, and (4) Hoagland solution without both nutrients. We followed the plants for three months and measured total biomass, aboveground biomass, root-to-shoot ratio, height, cotyledon persistence, appearance of the first pair of leaves, and leaf area. Growth of both species was sensitive to nitrogen availability. Supplemental phosphorus increased values of all traits in forest species but decreased some trait values in the savanna species. Except for root-to-shoot ratio and height which were higher in H. impetiginosus, the values for the other traits were consistently higher in H. aureus. The savanna species was more efficient overcoming N and P deficiencies. The two species were already ecologically distinct at early stages of development, which may be related to their evolutionary history regarding nutrients availability.