Abstract
This study has been primarily concerned with assessing a number of mycorrhizal fungi for their potential use in nursery inoculation of forest tree seedIings. This assessment has been accomplished using glasshouse and laboratory tests to determine the effects of the mycorrhizal fungi on the growth and nutrient status of Sitka spruce seedlings, and possible reasons for these effects. The importance of the soil in this relationship has also been considered. The glasshouse bioassays have shown that mycorrhizal fungi isolated from forest environments have a more beneficial effect on seedling growth in forest soils, whilst mycorrhizal fungi from forest nurseries improve seedling growth to a greater extent in nursery-type soils. Significant differences in effects on plant growth and nutrient status have been demonstrated not only between different fungal genera, but also between species of Laccaria and between isolates of Thelephora terrestris (Ehrh.) Fr. obtained from different environments. The relationship between growth, nutrient and mycorrhizal status of seedlings and the availability of nutrients in soil suggests that the availability of phosphorus in particular plays an important role in the success of the mycorrhizal association. Furthermore, it appears likely that the adaptation of mycorrhizal fungi to the availabiIity of phosphorus in their respective natural habitats may have an influence on their differing abilities to improve growth and nutrient status of seedlings grown in the different soil types used in this study. Finally, the value of the various techniques used for assessing the mycorrhizal fungi is also considered.