Abstract
The effects of acid precipitation and of soil pH on the formation of Picea sitchensis mycorrhizas have been studied. Discrepancies in soil pH found using different methods of measurement led to an investigation of soil pH methodology. Differences in soil preparatory technique and in the make of electrode used gave rise to significantly different pH measurements. A standardised and reproducible method of soil pH measurement was developed and is described. Fungi were isolated from sheathing mycorrhizal roots. Methods of isolation were compared. A method is described giving an isolation success of 0 to 70% (average 30%) comparing favourably with literature methods. Fungal isolates were used to synthesise mycorrhizas aseptically. Amanita rubesaens ((Pers.) Fr) S. F. Gray, Laccaria amethystina (Bolt, ex Fr.) Berk, et Br., Laccaria laocata (Scop, ex Fr.) Cooke, Thelephora terrestris (Ehrh) Fr; and Cenococcum geophilum Fr. formed mycorrhizas in pure culture. Those of the latter three species are described. Fungal isolates were used in pure culture linear growth experiments to establish the optimum pH for growth. A correlation between the pH for optimal growth and that of the soil of origin was observed for those fungi isolated from neutral soils. The incorporation of indicators into the agar as a quick and reliable method of substrate pH assessment was investigated. Simulated acidified rainfall and mycorrhizal inoculation both had a significant effect on seedling growth in a greenhouse pot experiment. However, the soil effect was so strong that the former effects were masked.