Abstract: Aluminum toxicity is a primary limiting factor for plants grown in acidic soils. Some ectomycorrhizal (ECM) fungi may improve the tolerance of their host plants against Al toxicity mainly by enlarging the uptake scope of nutrients, enhancing the availability of mineral nutrients, and/or inhibiting Al uptake by the host. Although these benefits have been partly illustrated in some ECM fungus species in vitro or in hydroponic or sand culture experiments, most focused on rhizoshere and fewer studies have examined the roles in field, and the transportation of nutrients and Al in plants still remained unclear.[Objective] In order to learn about the Al-tolerance of ectomycorrhizal seedlings, to select excellent ones, and to explore the nutritional mechanism,[Method] three isolates of Laccaria bicolor, namely Lb S238 A, Lb S238N and Lb 270, respectively, were used to inoculate Pinus massoniana seedlings to evaluate the growth, uptake and distribution of nutrients and Al in plants under Al-exposure. The seedlings were pre-planted for 4 weeks in native acid yellow soil from a masson pine stand, and then irrigated weekly with Hoagland nutrient solution containing 0.0 or 1.0 mmol·L^-1 Al³⁺ supplied with Al₂(SO₄)₃·18H₂O at pH 3.8 for 12 weeks.[Result] Exposure to Al stimulated the growth and uptake of P, Ca, Mg, and Al of seedlings inoculated with Lb S238A,whereas inhibited the growth of seedlings inoculated with Lb S238N or Lb 270, and inhibited uptake of Ca and Mg of Lb 270 seedlings. However, inoculation with any of the three isolates improved the growth and uptake of P, Ca, and Mg, but reduced or maintained Al uptake of seedlings under Al-exposure, with Lb S238A the best, compared to nonmycorrhizal (Non-ECM) seedlings. Inoculation with Lb S238A increased the seedling's growth by 69.9%, P uptake by 68.9%, Ca uptake by 69.7%, and Mg uptake by 81.5% under Al-exposure. Meanwhile, the improvement on growth from inoculation with any of the three isolates mainly exhibited on stem and on needles, with higher increment on stem than on needles. Inoculation with Lb S238A or Lb S238N decreased Al concentrations in each part of the seedlings, and Lb 270 decreased that in roots and in stem, with higher decrement in stem than in roots and in needles; Lb S238A or Lb 270 decreased Ca concentration apparently in stem and in roots, respectively, but Lb S238N increased that in needles. Inoculation with any of the three isolates decreased P concentration in roots but increased that in needles, and reduced distributions of P, Ca, and Al in roots but promoted those in needles.[Conclusion] Inoculation with any of the three isolates of L. bicolor improved the Al-tolerance of masson pine seedlings through the following ways:1) enhancing the uptake of P, Ca, and Mg; 2) reducing the distribution of P and Ca in roots and proceeding them upward to the stem and needles; 3) inhibiting or maintaining Al uptake and diluting Al concentration to a non-toxic value in seedlings. Among the tested three isolates, Lb S238A should be the best for masson pine seedlings to plant in acidic and allitic soils, and Lb S238N or Lb 270 should be suitable in acidic soils containing less aluminum. It needs to explore the role of ECM fungus on mechanism about transporting of nutrients and Al in ECM seedlings exposed to Al in the further study.

Key words: Laccaria bicolor, aluminum toxicity, nutrient, Pinus massoniana