This experiment was carried out in the Department of Soil Science of the Federal University of Viçosa, Minas Gerais State, Brazil, with the objective of evaluating the effect of P concentration and the duration of the P-omission period on three different fractions of P in Eucalyptus seedlings: i) total soluble P (TSP); ii) inorganic P (IP); and iii) organic P (OP). A solution containing high amount of phosphorus (8 mg L-1 of P) was added to five species of Eucalyptus (E. clöeziana, E. grandis, E. pellita, E. pilularis and E. urophylla) during 24 hours. After this period, P was totally eliminated from the nutrient solution, and the fractions of TSP, IP and OP were analyzed at 0, 10, and 20 days after the omission of the nutrient. Basal and apical leaves, as well as the extremity and basal portion of the root system, were analyzed for the different P fractions. Phosphate omission from the nutrient solution decreased the TSP and IP content in all species, though the magnitude of this decrease varied among species. Eucalyptus clöeziana presented the highest TSP content. As the P-omission period increased, the eucalypt species showed reduction in the percentage of participation of IP related to TSP, followed by a greater relative participation of OP in the different plant compartments. As the P-omission period increased, E. pellita and E. grandis showed a more gradual decrease in the IP/TSP ratio compared with the other species. However, E. pellita and E. grandis had smaller IP amounts at 10 days of P omission, which indicates a lower "IP internal buffer capacity" compared with the other eucalypt species.
phosphate fractions; eucalypt