Communities of P-solubilizing bacteria, fungi and arbuscular mycorrhizal fungi, were evaluated in two different ecosystems. Samplings taken from two areas of Atlantic forest, in Paraty -RJ, Brazil, one with a secondary forest and the other with a grass pasture were studied. Four growth media: GL (glucose and yeast extract), GES (glucose, soil extract, KNO 3 , CaCl 2 , MgSO 4 , NaCl, FeEDTA and micronutrients solution), GAGES (glucose, soil extract, arabinose, glycerol, CaCl 2 , MgSO 4 and NaCl) and GELP (glucose, soil extract, yeast extract, peptone, CaCl 2 , MgSO 4 and NaCl) were evaluated for the isolation of P-solubilizing microorganisms. The identification of P-solubilizing bacteria was based on 16 S rDNA sequence analysis, while the identification of P-solubilizing fungi and arbuscular mycorrhizal fungi was based on morphology. The greatest number of P-solubilizing bacteria was isolated using GL and GELP growth media. The greatest number of P-solubilizing fungi was isolated using GAGES and GES. The bacteria were identified as Enterobacteriaceae and Bacillus sp., while the P-solubilizing fungi were identified as Aspergillus sp. Glomus macrocarpum and Glomus etunicatum were the dominant mycorrhizal fungi in the secondary forest and grass pasture area, respectively.

This study evaluated the synergism between several P-solubilizing fungi isolates and arbuscular mycorrhizal fungi to improve clover (Trifolium pratense) growth in the presence of Araxá apatite. Clover was sown directly in plastic pots with 300g of sterilized washed sand, vermiculite and sepiolite 1:1:1 (v:v:v) as substrate, and grown in a controlled environment chamber. The substrate was fertilized with 3 g L −1 of Araxá apatite. A completely randomized design, in 8 × 2 factorial scheme (eight P-solubilizing fungi treatments with or without arbuscular mycorrhizal fungi) and four replicates were used. The P-solubilizing fungi treatments consisted of five Brazilian P-solubilizing fungi isolates (PSF 7, 9, 20, 21 and 22), two Spanish isolates (Aspergillus niger and the yeast Yarowia lipolytica) and control (non-inoculated treatment). The greatest clover growth rate was recorded when Aspergillus niger and PSF 21 were co-inoculated with arbuscular mycorrhizal fungi. Aspergillus niger, PSF 7 and PSF 21 were the most effective isolates on increasing clover growth in the presence of arbuscular mycorrhizal fungi. Greater mycorrhizal colonization resulted in greater clover growth rate in most PSF treatments. PSF 7 was the best isolate to improve the establishment of mycorrhizal and rhizobia symbiosis.