The use of microbial and organic amendments in the revegetation of smelter-affected soils near Flin Flon, MB

Abstract

The boreal forest area around Flin Flon, MB, and Creighton, SK, has been the site of a metal mining and smelting complex since the 1930s. Smelter emissions, coupled with forest logging, forest fires, and subsequent soil erosion, have led to severe vegetation dieback and the development of soils containing a mixture of metals in varying concentrations. In affected areas, existing vegetation typically is stunted. Limestone applications to affected soils have served to increase pH and, in some instances, the vegetation has responded positively; however, in some areas limestone application has failed to restore vegetation, leading to an interest in examining the suitability of other soil amendments to affect revegetation in these areas. Typically revegetation programs focus on aboveground vegetation responses; however, healthy plant growth often is dependent on the presence of an equally healthy soil microbial community. Thus, this study attempted to link revegetation success with responses of the soil microbial community structure to various soil amendments. Two studies were conducted to determine the influence of soil amendments (biochar, municipal and manure compost, glauconite, and an arbuscular mycorrhizal/ectomycorrhizal inoculant) on plant growth and microbial community structure in two soils from the Flin Flon area, classified as containing high and low metal concentrations. The two studies evaluated the growth of boreal forest understory species American vetch (Vicia americana) and tufted hairgrass (Deschampsia caespitosa) and overstory species jack pine (Pinus banksiana) and trembling aspen (Populus tremuloides) after addition of soil amendments, and the subsequent effects on microbial community structure. Greenhouse experiments evaluated plant growth for a period of 8 weeks (understory species) or 19 weeks (overstory species), after which plants were analyzed for changes in biomass and metal accumulation in plant tissue. Soils were analyzed for available metal concentrations, as well as microbial biomass carbon and nitrogen, and phospholipid fatty acid concentration, which is a measure of microbial community structure. Significant effects were seen on plant growth and microbial community structure due to the metal concentrations in the soil, but no one amendment consistently impacted plant growth or metal uptake, or any measured microbial parameter. The results of this study indicate the variability of plant growth and microbial functioning in soils from the study site, as well as the inherent challenges associated with revegetating heavy metal affected soils, and underline the need for further research on plant growth and microbial community structure at this site.