| Aluminum toxicity is generally considered to be the most important stress factor for plants grown in moderately to highly acidic soils.Al3+ is widely present in acid soils with pH<5.5 which eventually restraints plant growth and leads to the decline of forest productivity.Ectomycorrhizal fungi(ECMF)are the important component of forest ecosystems.Some of them can promote tree growth,stimulate nutrient absorption,and enhance the tolerance to aluminum stress.To better understand Al resistance mechanisms by ECMF under acid A1 stress,Pt715(Pisolithus tinctorius 715),and Ld 2,Ld 3(two strains of Lactarius deliciosus(L.Fr.)Gray)were selected for this study,under Al stress on ECMF growth,active aluminum species and enzyme activity of strains were studied to provide a theoretical basis for the restoration of forest decline caused by the acid deposits and healthy and sustainable management of forest ecosystems.The main conclusions were as follows:(1)In relation to aluminum tolerance ability ingeneral,Ld 2 showed maximum tolerance with respect to growth,and Pt 715 and Ld 3 also showed considerable tolerance to aluminum stress.The mycelial biomass of the 3 strains fungi increased as the concentration of A1 increased in the culture medium.When the concentration of Al was 2.0 mmol.L-1,biomass of Ld 2 was up to 53.48mg,which was 35.55%higher than non-Al-adapted.When the concentration of Al was 2.0 mmol.L-1,biomass of Pt 715 and Ld 3 were respectively 5.87%and 22.50%higher than non-Al.The average grrowth rate of Ld 2 also was the highest,which was up to 2.33 mg.d-1,Significantly higher than Pt715 and Ld 3,Were 1.97 times than Pt 715 and 1.85 times than Ld 3.The average growth rate of Ld 3 was 1.26 mg.d-1,The average growth rate of Pt 715 was close to Ld 3,was 1.18 mg.d-1.Ld 2 had the strongest anti-Al and fastest growth.(2)Ld 2,Ld 3 and Pt 715 have characteristics of aluminum hyperaccumulation.The concentrations of Al in Ld 2 at high-Al and medium-Al was 3.71 and 1.86 times as much as low-Al-adapted,for Ld 3 was 3.11 and 1.92 times,and for Pt715 was 2.89 and 1.86 times.There were no significant difference among the 3 stains fungi in relation to aluminum absorption at medium-Al,but were respectively 19.5%and 16.8%higher than Pt 715 at high-Al.Showed that two strains of Lactarius deliciosus on the ability of aluminum accumulation was stronger than Pt715.(3)When the aluminum was absorbed into the mycelium,the active aluminum species have significant difference with the change of Aluminum concentration and strains.Overall,the Content of Acid-soluble inorganic aluminum and humic-acid aluminum was higher than exchangeable aluminum and unimer hydroxyl aluminum.The average exchangeable aluminum in the three strains ranked as Ld 3(0.044)>Pt 715(0.027)>Ld2(0.016),unimer hydroxyl aluminum ranked as Ld 3(0.031)>Ld 2(0.023)>Pt 715(0.022),Acid-soluble inorganic aluminum ranked as Ld 2(0.487)>Pt715(0.463)>Ld3(0.363),humic-acid aluminum ranked as Ld 3(0.113)>Pt 715(0.079)>Ld2(0.014).under the concentration of high aluminum,middle aluminum and low aluminum,the higher activity form aluminum in the four kinds of active forms aluminum and the four kinds of active forms of aluminum in total Aluminum all ranked as Ld 2<Pt 715<Ld 3?Show that when the aluminum was absorbed into the mycelium,most of them presence as non-toxic or low toxic shape,Ld 2 had the strongest ability of aluminum conversion,Ld 3 was weakest,and with the increasing of aluminum concentration the ability of aluminum toxicity conversion was increased.(4)The enzyme activity of strains have significant difference with the change of Aluminum concentration.The average SOD Activity in the three strains ranked as Ld 3(248.98)>Pt715(171.10)>Ld2(137.40).The average POD Activity in the three strains ranked as Pt 715(328.70)>Ld3(96.99)>Ld2(49.68),The average CAT Activity in the three strains ranked as Pt 715(1.61)>Ld2(0.57)>Ld3(0.36).The change range of enzyme activity in Pt 715 was higher than Lactarius deliciosus with the change of A1 stress,showed that the enzyme activity in Pt 715 was more sensitive to the change of aluminum than Lactarius deliciosusIn short,the three strains of ECMF(Ld2,Ld 3 and Pt715)had strong resistance(tolerance)to acid Al in Southwest acid aluminum forestry district.The growth of the 3 strains fungi was promoted with the increase of Aluminum stress.They have the ability of aluminum accumulation,most of absorption of aluminum was converted into low or no toxicity form,and the activity of antioxidant enzymes were increased.In the three strains,Ld 2 had the strongest growth rate,biomass and the ability of aluminum conversion,and also had lowest sensitive to the change of aluminum.The results showed that Ld 2 had the best considerable tolerance to aluminum stress. |
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