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UBC Theses and Dissertations

Restoring grasslands in southern Ontario sandpits : plant and soil food web responses to arbuscular mycorrhizal fungal inoculum, biochar, and municipal compost Ohsowski, Brian Matthew


Habitat destruction and land use change are among the anthropogenic influences affecting many ecosystems. Sandpit mining often restricts grassland plant restoration efforts due to the abioticially stressed mine substrate, a lack of viable plant symbionts, and disrupted multi-trophic interactions in soil food webs. Recently excavated sandpits can be ameliorated with soil amendments and arbuscular mycorrhizal fungal inoculum to address these degraded substrate conditions, potentially improving plant performance and accelerating soil food web development. This dissertation describes the results of a multi-year grassland restoration project established in southern Ontario that optimized industrial-scale grassland restoration protocol in post-extraction sandpits. This research tested the effect of soil amendment rate (municipal compost, biochar) and arbuscular mycorrhizal (AM) fungal inoculum (Rhizophagus irregularis) in a grassland plant plug trial and a seed application trial. In the plant plug trial, the multi-year effects of the experimental treatments on plant growth, AM fungal colonization of roots, soil microbial biomass (i.e. bacteria and fungi) and soil animal abundance (i.e. nematodes, Collembola, and mites) were explored over two growing seasons. In the plant plug trial, 20T ha-¹ (tons hectare-¹) of compost mixed with a low rate of biochar (10T ha-¹) yielded the largest positive effect on total plant biomass, microbial community biomass, and soil animal abundance after two growing seasons. AM fungal inoculation did not influence total plant biomass or soil food web development during this trial. In the seed application trial, the multi-year effects of increasing rates of compost and biochar (0T ha-¹ to 40T ha-¹) were explored for total plant cover over three growing seasons. AM fungal inoculation combined with high rates of compost (20T ha-¹ and 40T ha-¹) and biochar (20T ha-¹ and 40T ha-¹) resulted in the highest plant cover over three growing seasons compared to controls. Our results indicate that: (1) co-amending mine substrates with compost, biochar, and AM fungal inoculum are practical land management tools that improve grassland plant growth while increasing soil food web development, (2) AM fungal inoculum increases plant cover when applying seed with high rates of compost + biochar, and (3) amending post-mine substrates with biochar as a solitary amendment may increase biotic stress in the sandpit environment during restoration. I suggest that restoration practitioners emphasize soil community development in tandem with plant community growth when restoring sandpits to maximize restoration success.

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