Potential Contribution of Native Herbs and Biological Soil Crusts to Restoration of the Biogeochemical Nitrogen Cycle in Mining Impacted Sites in Northern Canada

Abstract

The nitrogen cycle is highly sensitive to pollutants and restoration of this biogeochemical pathway is essential to ensure long-term sustainable ecosystems. Due to their ability to fix nitrogen, some native herb species and Biological Soil Crusts (BSCs) may promote plant community growth and help to establish primary successional processes. In a greenhouse trial, growth and nitrogen fixation rates of yellow mountain aven ( Dryas drummondii ), alpine sweetvetch ( Hedysarum alpinum ), field locoweed ( Oxytropis campestris ) and arctic lupine ( Lupinus arcticus ) were determined in tailings and mining impacted soils with amendments of Rhizobia and biochar. In a growth chamber trial, Pure Nostoc commune culture, Dried Nostoc spp. and BSC slurries derived from mature soil crusts were applied with and without biochar to tailings. Arctic lupine had the highest biomass and all species except yellow mountain aven showed nitrogen fixation in tailings and mining impacted soils. Nodulation and nitrogen fixation only occurred in herbs given a Rhizobia inoculum, suggesting the use of nitrogen-fixing species in northern reclamation may require microbial amendments. When used in combination with Rhizobia inoculum, biochar may promote nitrogen fixation associated with herb species. BSC slurries from mature soil crusts had significantly higher mean rates of nitrogen fixation (95μmol N m2 /hr) compared with other soil crust species (5–23μmol N m2 /hr). Biochar, Rhizobial inoculants and native nitrogen fixing species can enhance revegetation and nitrogen input in northern mining impacted substrates. However, large scale field experiments are required to identify suitable landscapes and determine how these initial nitrogen fixing species influence subsequent succession.