TEMPORAL CHANGES AND EFFECTS OF AMENDMENTS ON THE OCCURRENCE OF SHEATHING (ECTO-) MYCORRHIZAS OF CONIFERS GROWING IN OIL SANDS TAILINGS AND COAL SPOIL

The effects of peat, mineral fertilizer and sewage sludge on tree growth and mycorrhizal status were monitored after planting replicate enclosures containing oil sands tailings with container-grown jack pine (Pinus banksiana Lamb.) and subalpine coal mine spoil with white spruce (Picea glauca (Moench) Voss). Growth was generally better on coal spoil than oil sands tailings. Adding sewage sludge greatly increased growth of jack pine and both sewage sludge and peat improved the growth of white spruce. Populations of sheathing mycorrhizas on "egressed" roots were monitored for 10 years by direct observation and isolation techniques. The proportions of short roots of jack pine that were mycorrhizal ranged from 5 to 25% in Year 1, from 24 to 74% in Year 2 and from 29 to 91% in Year 4; their development was highest in the peat treatment and lowest in the fertilizer and unamended "control" treatments. Mycorrhizas of white spruce developed much more rapidly in coal mine spoil than those of jack pine in oil sands tailings: approximately 90% of short roots were mycorrhizal in coal spoil after 2 years irrespective of treatment. Thelephora terrestris was the dominant fungus on pine for the first 4 years except when growing with peat amendments when E-strain (Complexipes) dominated. Later Suillus spp. became more important, until after 10 years 32% of mycorrhizas were formed by Suillus. The early stage fungi, E-strain and T. terrestris, persisted and formed 23 and 17% of mycorrhizas after 10 years, respectively. In contrast to events on pines in oil sands tailings, E-strain fungi formed nearly all spruce mycorrhizas for the first 2 years; it was not until seedlings were 4 years old that E-strain began to be replaced by Amphinema byssoides (Fr.) J. Erikss. By Year 7 A. byssoides dominated all treatments (62-90%), but thereafter its abundance decreased. In Year 10, the dominant fungi on spruce were A. byssoides (19%), Hebeloma (19%), E-strain (25%) and Tomentella spp. (14%). These temporal changes suggest that the fungi forming mycorrhizas with jack pine and white spruce are subject to replacement in an ordered sequence that was not significantly affected by soil amendments or vigor of the host. Relatively few fungi were involved and late stage fungi were absent. The symbiotic mycoflora was species poor even after 10 years. The spectrum of fungi encountered is thought to be typical of mycorrhizas developing in non-forest soils.