Abstract:

Growth, oxalate efflux, and nitrogen, phosphorus and potassium uptake, by isolates of four ectomycorrhizal species:Lactarius deliciosus (Agaricales), Suillus luteus(Agaricales), Suillus grevillei (Agaricales) and Cenococcum geophilum (Eurotiales) were compared in pure culture in liquid media with variable concentrations of Al³⁺ (0, 0.20, 0.40 and 1.00 mmol·L^-1). The growth of the four ectomycorrhizal species were negatively but variably affected by Al³⁺. The two isolates originating from acidic soils in southwest China (L. deliciosus and Suillus luteus) showed less reduction in biomass compared to S. grevillei and C. geophilum originating from calcareous soils in northwest China. L. deliciosus and S. luteus also produced high oxalate accumulation in the culture solution with and without addition of Al³⁺. This could be beneficial to the fungi in reducing the concentrations of active Al³⁺ in culture solutions through the formation of chelate. In most cases of Al stress, higher accumulations of nitrogen, phosphorus, and potassium were observed in the mycelium of S. luteus and L. deliciosus than in S. grevillei and C. geophilum . Taking into account of higher biomass and larger nutrient absorption under Al exposure, S. luteus and L. deliciosus , indicating higher Al resistance of the fungal isolates from acidic soils than those from the calcareous, could be due to evolution and natural selection in acidic conditions. Furthermore, appropriate Al³⁺ in culture medium also increased in phosphorus concentrations in all of four fungal isolates, which could be one of beneficial patterns to precipitate intracellular Al³⁺ and diminish Al toxicity.

Key words: ectomycorrhizal fungi, aluminum, oxalate, nutrient