Research On The Response And Tolerance Mechanism Of Ectomycorrhizal Fungi To Aluminum Toxicity In Low PH Condition

Aluminum toxicityis generally considered to be the most important stress factor for plants grown in moderately to highly acidic soils. Aluminum may induce deficiency of nutrients such as Ca, Mg, P and K in plants. Addition of Al also results in precipitation of Al-Pi thereby creating P limitation. In forest ecosystems, mycorrhizas play an important role in mineral nutrition of higher plants and they may affect the response of trees to Al. The growth of mycorrhizal fungi can be inhibited or stimulated by Al, depending on the fungal species and the concentrations of Al used. For this reason, the study of the influence of Al on growth and mineral nutrition of ectomycorrhizal fungi seems to be a prerequisite for studies aiming to use ectomycorrhizal inoculation to improve Al tolerance of forest trees grown in degraded and wastelands. The results of this study are as follows:(1) In relation to aluminum tolerance ability ingeneral, Ld2showed maximum tolerance with respect to growth, and Pt715and Ld3also showed considerable tolerance to aluminum stested. The mycelial biomass of the3strains fungi increased as the concentration of Al increased in the culture medium. When the concentration of Al was2.0mmol·L-1, biomass of Ld2was up to52.43mg, which was36.31%higher than non-Al-adapted. There were no significant difference with the biomass of Pt715and Ld3, but which in2.0mmol·L-1-Al-adapted were respectively5.97%and14.67%higher than non-Al. The aluminum tolerance ability of the3stains fungi was sequenced as:Ld2>Ld3>Pt715, and the average growth rate of Ld2also was the highest,which was up to2.19mg. d-1(2) There were significant difference among the3stains fungi in relation to metal uptake. The concentrations of Al in Ld2and Ld3had no significant difference, but were respectively63.5%and48.7%higher than Pt715. The concentration of Al in Pt715increaseed linearly with the concentration increase of exogenous Al, while that of Ld2and Ld3performed exponential increased. The different mode of Al accumulation between the fungi may be the reason their different ability to Al-absorption. The phosphorus content of3strains of mycelium were significantly positively related to Al, while the potassium content showed significantly negative correlation to Al. The decreasing range of the concentration of potassium was sequenced as:Ld3(53.19%)>Ld2(34.74%)>Pt715(27.28%).(3) The secretion content of each strains of ECMF was significant differences. The secretion of H+first decreased and then increased correlated with the concentration of Al, where the secretion of H+of Pt715at high-Al was17.49times as much as low-Al-adapted, for Ld2was2.69and for Ld3was6.99times. Ld2secreted oxalic acid and formic acid when in the aluminum stress. Pt715and Ld3secreted oxalic acid,formic acid, succinic acid and tartaric acid when in the aluminum stress.(4) The cationic adsorption capacity of Ld2and Be were both great, and the absorption of Al was in accord with the Michaelis-Menton Equation.The CEC of Ld2was4.16times as much as Be. The Km of Ld2was21.63μmol·L-1,and that of Be was21.40μmol·L-1.