Phosphorus (Pi) suppression and resupply effects were studied on nitrogen biological fixation (N2) in alfalfa cv. Florida 77 inoculated with Sinorhizobium meliloti in different vegetative (V3 and V4) and reproductive (R6 and R8) stages. The experiment was carried in greenhouse and the plants cultivated in nutritive solution. The inorganic phosphorus (Pi) ten days suppression period decreased Pi levels in leaves and nodules in all growth stages, whereas in the roots this decrease was observed only in the vegetative stages. After Pi resupply to the nutritive solution during a similar period, ten days, it was observed Pi levels recovery in stages R6 and R8 for leaves, V3 and V4 for roots and V3 for nodules. Pi suppression altered the N2 fixation process as estimated by total aminoacids concentration in leaves and roots. Aminoacids levels in leaves and roots were significantly lower in plants under Pi suppression when compared to control plants. After resupply total amino acids levels in roots, throughout all growth stages, reached similar values to control plants, while in leaves this only happened in vegetative stages. Pi suppression did not influence the proportion of free aminoacids in the xylem sap.
Medicago sativa; aminoacids; nutritive solution; phosphorus metabolism
