Mycorrhizal studies regarding the reclamation of oil sand tailings: Production and outplanting of jack pine seedlings and amounts of VA- and ectomychrrhizal inoculum in stockpiled peat

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  • The major objectives of the ectomycorrhizal studies were to produce mycorrhizal jack pine seedlings in the greenhouse and to initiate a field study on the Syncrude dyke on the effect of different ectomycorrhiza1 fungi on the growth of jack pine. In addition, a simple inoculation technique which would allow inoculations to be performed under operational conditions was to be tested as well as the effect of different fertilizer levels on seedling growth and ectomycorrhizal development. These studies would then indicate the feasibility and limitations of inoculating with specific fungi and give information on the field performance of both fungi and pine seedlings in an actual reclamation situation. Under current practices, ectomycorrhizal tree species may acquire their symbionts while in the nursery, from the reconstructed soil they are planted in, or through air-borne sources after outplanting. VA mycorrhizal shrubs are dependent upon the same sources whereas plants seeded directly are totally dependent upon the reconstructed soil for inoculum. As a first step in evaluating the importance of these inoculum sources, an objective of the current study was to determine the relative amount of both ectomycorrhiza1 and VA mycorrhizal inoculum in undisturbed muskeg and in stockpiled muskeg. In that fungi differ in their effects on plant growth, identification of the symbionts was also attempted. The specific studies reported here are (1) the production of ectomycorrhizal jack pine seedlings under experimental conditions, (2) the outplanting of these seedlings on the Syncrude dyke and the first season's results, (3) the testing of near-operational fertilizer regimes on mycorrhizal development in the greenhouse, (4) the use of a simple slurry technique for inoculating seedlings, (5) the use of a bioassay technique to determine the effects of stockpiling muskeg peat on ectomycorrhizal and VA mycorrhizal inoculum, and (6) a comparison of ectomycorrhiza1 . development in the field and in the greenhouse to test the validity of the bioassay technique. The jack pine seedlings produced in the greenhouse were below the normal nursery target size due to the low fertilizer regime. However, the use of low nutrient levels permitted mycorrhizal development by 9 of the 12 fungi tested. The most aggressive fungi (those producing the highest levels of short root infection were Thelephora terrestris, Laccaria proxima, Hebeloma sp. and E-strain. All of these are known as \"weedy\" species and are commonly found in nurseries. A lower degree of infection was achieved with Cenococcum geophilum, Pisolithus tinctorius, Astraeus hygrometricus, Lactarius paradoxus and Sphaerosporella brunnea. Amphinema byssoides, Hydnum imbricatum and Tricholoma flavovirens failed to form any mycorrhizae. After one season in the field, T. terrestris, L. proxima, Hebeloma sp. and E-strain had all readily infected the new roots that extended into the reconstructed soil. The other fungi were poor colonizers of jack pine roots in the field. Competition from indigenous fungi was not a factor in the degree of success as only 4% of the short roots were infected by indigenous species. Growth of jack pine was not significantly affected by the presence of mycorrhizae during the first growing season. It was necessary to produce larger seedlings if inoculations were to have any practical value. In a fertilization experiment, it was found that E-strain fungi and Laccaria proxima would aggressively infect jack pine roots at approximately one-half the operational fertilizer rate. The seedling size was acceptable for normal outplanting. Pisolithus tinctorius and Sphaerosporella brunnea were more sensitive to high fertilizer rates than the former two fungi. The standard inoculation procedure requires that the inoculum be grown in a solid carrier several months prior to seeding the containers and that inoculation takes place as the growing medium is added to the containers. However, experimental evidence presented here shows it is also possible to use an easily prepared mycelial slurry which can be injected into the individual cells after the seedlings are two months old. The slurry infection technique proved to be just as effective as the solid carrier technique for aggressive species. The technique offers considerable time-saving advantages as well as simplifying experimental inoculations in operational nurseries. In the process of mining, the muskeg peat is stripped off and stockpiled until it is required for the reclamation of the tailings sand. The greenhouse bioassay used here clearly shows that the amount of ectomycorrhizal inoculum is reduced by stockpiling. It reduced infection levels of the jack pine test seedlings, resulted in fewer ectomycorrhizal seedlings and a strong reduction in the number of symbiont species present. The bioassay technique for ectomycorrhizal inoculum was effective at detecting viable mycorrhizal fungi but had limited quantitative predictive value for field situations. VA mycorrhizal inoculum was very rare in both undisturbed peat and peat stockpiled for 8 months. This was due to the rare occurrence of compatible hosts in muskeg plant communities. However, when stockpiles were seeded with grasses and legumes, there was a slow build-up of VA inoculum. From these studies it can be recommended that: 1) Monitoring of the ectomycorrhizal inoculation study on the Syncrude dyke be continued; 2) Strong efforts should be made to improve inoculation techniques, especially with regard to those fungi which consistently fail to survive in the growing medium. This will involve basic studies of survival mechanisms and microfloral interactions; 3) A wide range of potential symbionts should be tested for their sensitivity to a range of fertilizer regimes in the greenhouse; 4) In that VA mycorrhizal inoculum in peat is sparce, the mycorrhizal dependency of all VA hosts used in the reclamation of tailings sand should be determined; 5) The mycorrhizal condition of VA hosts planted on the Syncrude dyke should be evaluated to determine if the absence of inoculum is potentially limiting reclamation progress; 6) The development of indigenous ectomycorrhizal populations in the outplanting study should be followed and the effectiveness of these fungi evaluated; 7) The other major input of ectomycorrhizal inoculum should be evaluated. This would involve determining the species of fungi present on nursery stock, the degree of colonization of the roots, and the persistence of these fungi following outplanting; and 8) The use of mineral topsoil as a source of VA mycorrhizal inoculum should be evaluated. VA mycorrhizal hosts are common in aspen stands and the addition of a small amount of soil from these stands to reconstructed soils may be sufficient to establish VA mycorrhizal systems.

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