Effects of manganese on growth, nutrient uptake and organic acid exudation by ectomycorrhizal fungi.

Ectomycorrhizal fungi Cenococcum geophilum 04 (Cg 04), Pisolithus tinctorius 715 (Pt 715) and Suillus luteus 13 (Sl 13) were grown in liquid culture media to investigate the effects of manganese (Mn) on fungal growth, organic acid exudation (oxalate and acetate) and nutrient uptake (nitrogen, phosphorus and potassium). The results showed that Pt 715 had the highest biomass, followed by Sl 13 and Cg 04 was the lowest. Mn2+ was harmful to fungal growth and y=ax+b（a0）could express the relations between hyphae biomasses (y) and Mn concentrations (x) in the culture medium, where Mn2+ ranged from 0 to 800 mg/L. Less inhibition on the growth of Pt 715 and Sl 13 than Cg 04 under Mn stress suggests higher abilities of Pt 715 and Sl 13 against Mn toxicity. The reason for this could be explained by environmental adaptation and evolution for manganese resistance due to longterm survival in acidic soils with high available Mn. Moreover, both Cg 04 and Pt 715 exuded oxalate but not acetate into liquid culture media as Mn concentrations increased. In contrast, Sl 13 could release acetate, and the oxalate exudation rate decreased with increasing Mn concentrations. Therefore, the complexing of Mn with oxalate exuded by ecotmycorrhizal fungi might not be the sole biochemical pathway against Mn toxicity. More nitrogen, phosphorus and potassium were absorbed by Pt 715 and Sl 13 than Cg 04 In the culture media, particularly with high Mn concentration (800 mg/L), Cg 04 absorbed less nutrient (except nitrogen) than Pt 715 and Sl 13 The scale of nutrient uptake by Pt 715 and Sl 13 was 20.8%-15.44%(phosphorus) and 51.20%-27.27% (potassium) less than Cg 04 High nutrient uptake could benefit fungal cell health and Mn tolerance, which could also improve the ability of host plants for Mn resistance.