INJURIES TO SCOTS PINE MYCORRHIZAS AND CHEMICAL GRADIENTS IN FOREST SOIL IN THE ENVIRONMENT OF A PULP-MILL IN CENTRAL FINLAND

The occurrence and condition of Scots pine mycorrhizas were studied at different distances from a pulp mill in Central Finland. The chemical analyses of the soil humus layer in the vicinity of the mill revealed increased levels of ammonium-nitrogen, sulphur and calcium but unalte red concentrations of phosphorus and magnesium. Higher nitrate levels and nitrification were clearly detected at some sites which had recent ly been limed. Significant decreases in root ramification index and nu mber of living mycorrhizas were found in a zone 0-0.6 km zone surround ing the factory but these parameters increased with increasing distanc e. Within a 2 km zone around the mill there were abundant Cenococcum g eophilum and Paxillus involutus-type mycorrhizas while lowered frequen cies of several other mycorrhizal types were detected. An ultrastructu ral study revealed changes in several types of mycorrhizas, the deares t of which were increased tannin deposition in cortical cells, intrace llular growth of hyphae in cortical cells and the appearance of electr on dense accumulations in the vacuoles of the fungal cells. The ultras tructural changes observed were distributed at least to a distance of 3 km from the mill and occurred in the roots of trees that had only a slight loss of needle mass. Nitrogen deposition is suspected to be the primary cause of root decline but atmospheric SO2 through the tree cr own is also likely to be a contributing factor.