The effects of arbuscular mycorrhizal fungi (AMF) and Rhizobium on P uptake and efficiency of use, as well as on the P fractions of Eucalyptus grandis grown in an intercropping system with Sesbania virgata were evaluated under greenhouse conditions. The treatments were: with or without inoculation with AMF of both plant species and with or without inoculation with Rhizobium of S. virgata plants only, in four replications. The two plant species were grown together in pots with a volume of 6 L for 100 days. Inoculations with AMF or with AMF + Rhizobium increased the P content in Eucalyptus plants, while inoculations with Rhizobium, AMF, or with AMF + Rhizobium increased the P utilization efficiency. An increase of total acid-soluble P (PTS) in the treatments inoculated with Rhizobium or AMF + Rhizobium was observed in the P fractions of the analyzed Eucalyptus plant leaves. In the inoculation treatments with Rhizobium, AMF, and AMF + Rhizobium, and the control (uninoculated) 81, 32, 91, and 68%, respectively, of the PST in the leaves of Eucalyptus plants were found in organic-P (Po) form. An evaluation of both the P fractions and P contents of Eucalyptus shoots suggests that the increase of PST and organic-P was caused by the inoculation of Rhizobium in sesbania plants, and not by the internal P plant content.
arbuscular mycorrhiza; legumes; symbiotic association; biological nitrogen fixation
