Can locally sourced inoculum and biochar synergistically improve the establishment of mycorrhizal fungi in mine tailings?

Authors: FREWERT, AUSTIN - Washington State University; Trippe, Kristin; CHEEKE, TANYA - Washington State University

Submitted to: Restoration Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/3/2021
Publication Date: 8/10/2021
Citation: Frewert, A., Trippe, K.M., Cheeke, T. 2021. Can locally sourced inoculum and biochar synergistically improve the establishment of mycorrhizal fungi in mine tailings? Restoration Ecology. 30(3). Article e13518. https://doi.org/10.1111/rec.13518.
DOI: https://doi.org/10.1111/rec.13518

Interpretive Summary: Severely degraded soils at abandoned mine lands (AMLs) are associated with severe environmental challenges that affect the surrounding ecosystems and communities. Restoration of these sites could be achieved by establishing plant communities, however, the extremely acidic, nutrient poor, and severely compacted soils limit plant growth. Biochar, or charcoal that is added to soils has been shown to alleviate some of the factors that constrain plant growth at AMLs. Similarly, mycorrhizal fungi, which generally benefit plant growth, improve the ability of plants to survive and proliferate in nutrient poor soils. Amendments that contain both biochar and mycorrhizal fungi may act synergistically to improve plant growth; however, the efficacy of these soil amendments for improving the establishment and survival of native plant species in ecological restorations is unpredictable. Planting the right plant species with the right amendment or amendment blends is crucial to the success of restoration goals. In the current study, we evaluated the growth responses of two plant species in tailings collected from the Formosa Mine (Riddle, Oregon). Seedlings of blue wildrye, a native grass, and Douglas Fir, a native conifer, were grown in tailings amended with biochar, locally-collected mycorrhizal fungi, a combination of biochar and mycorrhizal fungi, or in unamended tailings. We predicted that the individual and blended amendments would increase plant growth. Instead, the amendments had no effect on plant growth, and biochar by itself reduced the growth of blue wildrye. Despite the lack of growth response, we observed significant rates of mycorrhizal colonization in the plants amended with mycorrhizae, demonstrating that locally-sourced inoculum can survive and proliferate in the amended Formosa tailings. Thus, inoculated seedlings of native plant species could provide essential ground cover and long-term habitat for developing mycorrhizal communities in mine tailings.

Technical Abstract: Severely degraded soils at abandoned mine lands present several environmental challenges. Restoration of these sites could be achieved by establishing plant communities, however, the edaphic conditions at these sites— low pH, soil nutrient deficiency, and soil compaction— limit plant growth. Biochar and/or mycorrhizal fungi, may attenuate these constraints. However, the efficacy of amendments for improving the establishment and survival of native plant species in ecological restorations can be context dependent; pairing the right plant species with the right amendment or amendment blends is crucial to the success of restoration goals. In a full factorial greenhouse experiment, we evaluated the growth responses of two native plant species in soils collected from the Formosa Mine Superfund Site (Riddle, Oregon, USA). Seedlings of Elymus glaucus and Pseudotsuga menziesii were grown in tailings amended with biochar, locally-collected rhizosphere soil containing a suite of soil microorganisms including mycorrhizal fungi, a combination of biochar and rhizosphere soil, or in unamended tailings. We hypothesized that (1) individual amendments would increase plant biomass compared to controls and (2) that the co-amended treatments would have a synergistic effect on plant growth. Instead, we detected no effect of the rhizosphere soil or the co-amendment on the growth of either plant species and found that biochar reduced the shoot biomass and leaf chlorophyll content of E. glaucus. Despite the lack of growth response, we observed significant rates of mycorrhizal colonization in the plants amended with local rhizosphere soil, demonstrating that locally-sourced fungi can survive and proliferate in the amended Formosa tailings. Thus, inoculated seedlings of native plant species could provide essential ground cover and long-term habitat for developing mycorrhizal communities in mine tailings.