Effects of Artificial Acid Precipitation on the Mycorrhizas of Scots Pine Seedlings

Summary Roots were examined from three‐year‐old Scots pine seedlings (Pinus sylvestris L.) growing on a humo‐ferric podzol in monolith soil lysimeters which had received simulated acid rain at pH 3 or non‐acidified rain. This is about 30 times the rate of wet H+ deposition at the site from which the lysimeters were taken. Root biomass was similar between treatments, but acid‐treated root systems showed significantly reduced fine root branching compared to the controls. The reduced branching of acid‐treated root systems was attributed to a significant reduction in the occurrence of two corralloid mycorrhizal morphs. The coralloid mycorrhizas were characterized by profuse extramatrical hyphal development, the growth of which was retarded by soil conditions in the acid‐treated lysimeters. Soil solution measurements showed the major effects of the acid treatment to be increases in concentrations of H+, Ca2+, A1 and SO42−. It seems likely that an increase in Al and reduction of pH had affected the growth of these mycorrhizas. This may have nutritional consequences for trees on acidic soil.