A three season study was conducted to determine the effect of added composted yard waste, arbuscular mycorrhizal (AM) fungi, and fertilizer on plant cover, standing crop biomass, species composition, AM fungal infectivity and spore density in coarse taconite iron ore tailing plots seeded with a mixture of native prairie grasses. Plant cover and biomass, percent seeded species, mycorrhizal infectivity and spore density were greatly increased by additions of composted yard waste. After three seasons, total plant cover was also greater in plots with added fertilizer. Third season plant cover was also greater in plots amended with the higher rate (44.8 Mg ha -l) of compost than the moderate rate (22.4 Mg ha-l). Field inoculation with AM fungi also increased plant cover during the second season and infectivity during the first two seasons. Seeded native species, consisting mostly of the cover species Elymus canadensis, dominated plot vegetation during the second and third seasons. Dispersal of AM fungal propagules into nonmycorrhizal plots occurred rapidly and increased infectivity in compost-amended plots during the third season. In plots with less than 10% plant cover, AM fungal infectivity of inoculated plots was greatly reduced after the second season. The high level of plant cover and the trend of increasing proportion of mycorrhizal-dependent warm-season grasses, along with increases in infectivity, forecast the establishment of a sustainable native grass community that will meet reclamation goals.

SUMMARYIn a gliiashouse experiment using coarse taconite iron ore tailing as the substrate, we examined interactions between the warm-season grasses Aiidropogoii gcrardii (big bluestem) and Schi~achyrium scopariiwi (little bluestem), and the cool-season grass Elymiis canadeiisis (Canada wild rye), and indigenous arbuscular mycorrhizal (AM) fungi from an adjacent fine tailing basin. Shoot dry mass (DM), P uptake, shoot P concentration, root DM, root length, spore density, percentage root length colonized, and length of external AM fungal hyphae were measured over a gradient of phosphate availability. Andropogon gerardii was highly dependent and responsive to inoculation at low P, whereas inoculation had no significant effect on the growth of S. scopariinii. Root DM and root lengths of both warm-season grasses were unaffected by mycorrhizal inoculation. Eiyvuis caiiadeiisis was responsive only at the lowest P level and not dependent on mycorrhizas; in fact, shoot DM, P uptake, root DM and root lengths were all greater in control than inoculated plants at moderate P levels. Despite a growth suppression, colonized root lengths for E. canadeiisis were approximately five times longer than warm-season grasses at low P levels, making it suitable as an early succession species for increasing mycorrhizal inoculum potential and thus enhancing the successful reclamation of coarse tailing deposits by more persistent, mycorrbizaldependent species.

The effect of reclamation treatments on seeded native grass cover and species composition, soil microbial biomass carbon, and populations of actinomycetes, fungi, free-living N2-fixing bacteria, and aerobic heterotrophic bacteria was compared in field plots in coarse taconite tailing. Reclamation treatments consisted of all possible combinations of three rates of composed yard waste, three rates of fertilizer, and inoculation with arbuscular mycorrhizal fungi. Composted yard waste increased plant cover, soil microbial biomass, and populations of all groups of microorganisms compared with unamended, non-inoculated control plots. Microbial populations and biomass in tailing plots were low compared with natural soils and were correlated with plant cover and available P. Mycorrhizal inoculation resulted in a 6% increase in plant cover, although this was not significant, and significantly enhanced N2-fixer populations in June but did not affect other groups of microorganisms. There were no differences between moderate and high rates of composted yard waste. We conclude that incorporation of a moderate rate of organic matter can ameliorate the stressful conditions of coarse taconite tailing and can enhance the initiation of a functional soil ecosystem able to support the establishment of seeded native prairie grasses and may provide a long-term solution to reclamation of taconite tailing. Key words: arbuscular mycorrhizal fungi, mine reclamation, soil microorganisms, composted yard waste.

Abstract. Studies were initiated to determine the occurrence and rate of immigration of VAM spores into recently deposited coarse and fine tailings. Plant roots, soil, and coarse and fine tailings were collected every two weeks from May through September 1990 and analyzed for VAM species present, spore numbers, and percent root colonization. Average spore numbers ranged from 0.7 to 56/g soil and percent root colonization ranged from 4.4 to 18.4%. VAM species present were: Acau7ospora bireticu7ata, G7omus aggregatum, G. c7aroides, G. intraradix, and G. mosseae. G7omus intraradix was the most frequently recovered species from all sites. Field plots of seventeen pl ant species native to Minnesota were established to evaluate seedling establishment, growth, and survival. Half of the plots received 3 g root/soil inoculum of G. intraradix. One thousand seeds of each species were planted into one square meter plots. Ammonium nitrate fertilizer was applied to all plots at a rate equal to 220 kg/ha. Stand counts were taken 6 weeks after pl anting with the following results expressed as a percentage: Amorpha canescens 54, Andropogon gerardi 78, E7ymus canadensis 83, Lespedeza capitata 70, and Schizachyrium scoparium 57. A greenhouse study was conducted with these five plant species in combination with G. intraradix for the evaluation of its effect on plant biomass in coarse tailings. Plant biomass and colonization by G. intraradix were significantly greater than noninoculated plants. Additional

Aboveground production and shoot and root litter decomposition rates were measured in amended coarse taconite tailing plots over the second and third growing seasons of a 3‐yr study. Plots were seeded with a mixture of native prairie species that included Andropogon gerardii Vitm., Schizachyrium scoparium (Michx.) Nash, Elymus canadensis L., Bromus kalmii Gray, and Lespedeza capitata Michx. Reclamation treatments included inoculation with indigenous mycorrhizal fungi, three rates of fertilizer, and three rates of composted yard waste. Aboveground plant biomass in plots amended with 44.8 Mg ha−1 compost increased from 150 g m2 in the second season to 330 g m2 in the third season. The litterbag technique was used to assess the influence of reclamation treatments on the decomposition of plant litter. Shoot litter placed on the surface lost 60 to 70% of its original mass after 15 mo and was unaffected by treatment during the first season but was slower in plots amended with 44.8 Mg ha−1 composted yard waste in the second season. Buried root tissue lost 40% of its original mass after 15 mo and was unaffected by treatment. By significantly increasing plant biomass and reducing litter decomposition rate in tailing, additions of 44.8 Mg ha−1 compost should result in the continued accrual of soil organic matter and begin to meet reclamation goals to establish self‐sustaining native plant communities on tailing deposits.