Plant growth and arbuscular mycorrhizae development in oil sands processing by-products.

Soil pollutants such as hydrocarbons can induce toxic effects in plants and associated arbuscular mycorrhizal fungi (AMF). This study was conducted to evaluate if the legume Lotus corniculatus and the grass Elymus trachycaulus and arbuscular mycorrhizal fungi could grow in two oil sands processing by-products after bitumen extraction from the oil sands in northern Alberta, Canada. Substrate treatments were coarse tailings sand (CTS), a mix of dry mature fine tailings (MFT) with CTS (1:1) and Pleistocene sandy soil (hydrocarbon free); microbial treatments were without AMF, with AMF and AMF plus soil bacteria isolated from oil sands reclamation sites. Plant biomass, root morphology, leaf water content, shoot tissue phosphorus content and mycorrhizal colonization were evaluated. Both plant species had reduced growth in CTS and tailings mix relative to sandy soil. AMF frequency and intensity in roots of E. trachycaulus was not influenced by soil hydrocarbons; however, it decreased significantly over time in roots of L. corniculatus without bacteria in CTS. Mycorrhizal inoculation alone did not significantly improve plant growth in CTS and tailings mix; however, inoculation with mycorrhizae plus bacteria led to a significantly positive response of both plant species in CTS. Thus, combined inoculation with selected mycorrhizae and bacteria led to synergistic effects. Such combinations may be used in future to improve plant growth in reclamation of CTS and tailings mix.

The ectomycorrhizal morphotype Pinirhiza sclerotia is formed by Acephala macrosclerotiorum sp. nov., a close relative of Phialocephala fortinii.

Relatively few ectomycorrhizal fungal species are known to form sclerotia. Usually, sclerotia are initiated at the extraradical mycelium. In this study, we present anatomical and ultrastructural evidence for the formation of sclerotia directly in the hyphal mantle of the mycorrhizal morphotype Pinirhiza sclerotia. A dark-pigmented fungal strain was isolated from Pinirhiza sclerotia and identified by molecular tools as Acephala macrosclerotiorum sp. nov., a close relative of Phialocephala fortinii s.l. As dark septate fungi are known to be mostly endophytic, resyntheses with Pinus sylvestris and A. macrosclerotiorum as well as Populus tremula x Populus tremuloides and A. macrosclerotiorum or P. fortinii s.l. were performed under axenic conditions. No mycorrhizas were found when hybrid aspen was inoculated with A. macrosclerotiorum or P. fortinii. However, A. macrosclerotiorum formed true ectomycorrhizas in vitro with P. sylvestris. Anatomical and ultrastructural features of this ectomycorrhiza are presented. The natural and synthesized ectomycorrhizal morphotypes were identical and characterized by a thin hyphal mantle that bore sclerotia in a later ontogenetic stage. The Hartig net was well-developed and grew up to the endodermis. To our knowledge, this is the first evidence at the anatomical and ultrastructural level that a close relative of P. fortinii s.l. forms true ectomycorrhizas with a coniferous host.

Nutrient amounts of ectomycorrhizae analysed by EDX using ESEM and ICP.

Energy-dispersive X-ray (EDX) analysis coupled with an environmental scanning electron microscope (ESEM) was tested as an alternative to the inductively coupled argon plasma (ICP) spectrometer method for nutrient analyses of ectomycorrhizae. The results of EDX-ESEM and ICP were compared for 12 ectomycorrhizal morphotypes collected in beech and Scots pine forests in northern Brandenburg. The amounts of Al, Ca, Mg and S analysed in the outer hyphal layers of the sheath with the EDX-ESEM technique correlated well with the amounts of these elements in the whole mycorrhiza as assessed by ICP. For the elements P and K, no such correlation existed, indicating an uneven distribution of these elements in the ectomycorrhiza. It is concluded that the EDX-ESEM technique could be a useful and reliable tool for the analysis of nutrient elements in ectomycorrhizae, especially for studies focussing on small-scale soil heterogeneity or on infrequent morphotypes.