Biochar Promotes the Germination and Growth of Herbaceous Seeds Hydroseeded on Gold Mine Tailings

Tailings that are generated by gold mining activities are frequently abandoned to let nature initiate ecological succession processes. Given the slowness of natural processes, colonization mechanisms could be accelerated through assisted revegetation with herbaceous species as pioneer species prior to reintroduction of native woody species to stabilize them and reduce their transport in the environment. Application of biochar increasingly has been suggested as a means of supporting germination, emergence and growth of seedlings on mine tailings. In this study, we assessed the effects of two types of biochar on the germination and growth of Avena sativa, Festuca rubra and Trifolium repens that were hydroseeded onto waste rock and fine tailings from gold mining. The first biochar was made through pyrolysis of maple bark at 700 degrees C and the second biochar was derived from pyrolysis of hardwood chips (< 75% sugar maple), at temperatures of 500 degrees C. Seeds were placed separately on fine and waste rock tailings in 9-cm diameter Petri dishes and the germination test was conducted in a growth chamber. The growth mesocosm experiment was conducted in the greenhouse, where the three plant species were mixed in two hydroseeding ratios. In petri-plate tests, biochar application improved the germination of plant species, depending upon the type of biochar and plant species. Avena sativa best responded to biochar application, with the highest germination rate (up to 94%). In the greenhouse, plant growth in hydroseeding mixtures was also affected by biochar type. The first biochar (Award-Maple-700) enhanced root and aboveground biomass of plants in hydroseeding mixtures compared to the level without biochar. It also enhanced aboveground biomass of Festuca rubra and Trifolium repens individually compared to the level without biochar. However, the second biochar did not consistently enhance the growth of species. On one hand, these results underscore the potential for biochar to improve initial revegetation of mining residues using herbaceous species; on the other hand, its effect varies with both the type of biochar and plant species. Larger, longer term studies are recommended to test observed effects in situ, with the aim of revegetating gold mining tailings at operational scales.