Soil phosphorus pools and supply under the influence of Eucalyptus saligna and nitrogen-fixing Albizia facaltaria

Replicated plantations of Eucalyptus saligna (Sm.) and Albizia falcataria (L.) Fosberg were examined for patterns in soil phosphorus (P) fractions and soil P availability. The supply of P was assessed in the field with anion exchange resin bags, which indicated that P supply was about twice as high under Eucalyptus as under Albizia. In the laboratory, solution P extracted with iron oxide-impregnated paper strips was also 45% higher under Eucalyptus. The effects of mixtures of the two species were intermediate between the pure-species effects. Overall, P supply either increased with Eucalyptus or decreased under Albizia. Despite significantly lower soil P availability, the Albizia plots appeared to take up and cycle as much P as the Eucalyptus plots, indicating that P supply was not independent of P demand. High rates of P uptake by Albizia may depend on higher allocations of carbohydrate to belowground production.