Abstracts |
Mycelial biomass and protease, urease, nitrate reductase and chitinase activities of four ectomycorrhizal fungal isolates, viz. Cenococcum geophilum strain Cg SIV, Pisolithus tinctorius strain Pt715and two Lactarius sp. strains Ld-1 and Ld-3, were evaluated in pure liquid culture containing 0, 5, 50 or 150 micro mol/L Hg2+. Growth of fungal hyphae was restrained by mercury, whereas Cg SIV showed tolerance to Hg in some extent, with the least decrease on biomass. All of the four strains expressed protease, chitinase, urease and nitrate reductase, and showed significant differences in enzyme activities. It implied that ectomycorrhizal fungi might not only benefit to nitrogen utilization diversity of host plants, but also favored different nitrogen sources. Effects of Hg on activities of nitrogen utilizing enzymes in ectomycorrhizal fungi varied with strains, enzyme categories and Hg2+ concentration. Since the inherited characteristics differ among strains, enzyme synthesis may vary under condition of the mercury existence, and express allozymes with different sensitivity to Hg. Moreover, low to middle Hg concentration (5-50 micro mol Hg2+/L) promoted or did not affect the activities of nitrogen utilizing enzymes, suggesting that nitrogen utilization by ectomycorrhizal fungi might not be restraint or even be promoted. Activities of protease, urease, nitrate reductase and chitinase were the highest in Pt715 and Ld-3 with or without Hg treatment, which showed relatively high capacity of nitrogen utilization. Inoculating Pt715 and Ld-3 may improve nitrogen nutrition of eucalyptuses and pines planting in mercury contaminated soils. |