Elemental and Isotopic Perspectives on the Impact of Mycorrhizal Fungi on Mineral Weathering Across Imposed Geologic Gradients

Abstract:

Climate change and other environmental stressors have been shown to influence soil biology, weathering, and nutrient cycling in the “critical zone,” the area where rock meets life.  Symbiotic mycorrhizal fungi play a role in weathering by targeting required plant nutrients, such as phosphorus (P) and calcium (Ca), that are contained in minerals. Field experiments coupled with geochemical analyses provided insights on two important symbioses: arbuscular-mycorrhizal and ectomycorrhizal fungi. In-growth bags containing different rock types (granites of varying P content as well as carbonate bedrock) were fabricated to create an in-situ geologic gradient for deployment in the two different symbioses. We targeted the temperate mixed hardwood forest site of Hubbard Brook as well as the subarctic birch forests of Abisko, Sweden. Both sites contained vegetation with known ectomycorrhizal and arbuscular mycorrhizal fungal symbioses. Weathering productivity under varying fungal type and mineral substrate, determined via elemental and isotopic proxies, was assessed in terms of mineral decomposition reactions (particularly apatite and biotite breakdown). Forthcoming metagenomic analyses will help to further illuminate impacts of bedrock composition on the fungal community and could provide greater insight into the influence of these factors on weathering processes.