EFFECTS OF ALUMINUM AND PH ON GROWTH AND POTASSIUM UPTAKE BY 3 ECTOMYCORRHIZAL FUNGI IN LIQUID CULTURE

Soil acidification and Al toxicity may be important factors in the decline in vitality of many forest trees and the associated ectomycorrhizal fungal flora. In this study, effects of low pH and high Al concentrations were investigated on both growth and K+ uptake by three Douglas-fir ectomycorrhizal fungi in solution culture. In growth experiments, Lactarius rufus and Lactarius hepaticus appeared to be tolerant to low pH but sensitive to Al. In contrast, Laccaria bicolor exhibited high Al tolerance and high sensitivity to acidification. Al toxicity in both Lactarius isolates was alleviated by an increase in the orthophosphate concentration from 20 to 120-mu-M, whereas it was not influenced by an increase in Ca concentration. Elevation of the Mg concentration alleviated Al toxicity in Lactarius rufus, but not in Lactarius hepaticus, although growth was stimulated in this fungus. Net K+ uptake by a 2-week-old (log phase) mycelium was determined as function of both Al and medium pH, at a K+ concentration of 100-mu-M. The fungal species each exhibited specific pH optima for K+ uptake. At pHs below 4, K+ uptake rate was decreased in each species. High Al concentrations severely inhibited K+ uptake in Lactarius hepaticus, but not in the other species.