| Plant-fungal associations are important in every ecosystem, because 95% of land plants live with mycorrhizal fungi, which increase nutrient acquisition and weathering. In this study, the effect of vascular vegetation and ectomycorrhizal fungi was examined on chemical weathering and denudation fluxes at the scale of the Hubbard Brook sandboxes (Chapter 1) and in column growth experiment (Chapter 3). Fungal weathering mechanisms were also tested in liquid-culture experiments (Chapter 2).; The main approach was a simple mass-balance on base cations (Ca, K and Mg). All three designs allowed us to measure input and output water flows and concentrations, change in biomass and on soil-exchangeable cation sites. Microscopic investigation of microbe-mineral interface and mineral surface changes were carried out to understand weathering and denudation mechanisms on small scales.; Both geochemical and ecosystem-ecological perspectives were employed to better understand temporal dynamics of the effect of red pine on weathering and denudation fluxes of the sandboxes. Three periods were distinguished during the ecosystem development and disturbance: weathering-driven (large weathering and retarded denudation); biocycling-driven (tree regulated weathering and denudation); and denudation-driven (after tree-harvest with lost regulation on processes) nutrient dynamics.; In liquid-cultures direct surface attachment of fungal hyphae to mineral surfaces did not prove to be important and the fungi did not directly transport K and Mg into biomass and did not leave dissolution channels behind, as it was hypothesized from previous microscopic results of sandbox minerals. Fungi indirectly induced weathering by lowering the solution pH via production of complex forming organic acids. In addition, most of the weathered mass came from the edges.; The column experiment demonstrated that bacteria and ectomycorrhizal fungi had large potential to weather Ca-bearing minerals, but microbes could not regulate denudation losses without a vascular host. In the second half of the experiment highest weathering and lowest denudation were observed in ectomycorrhizal tree-treatments, but non-ectomycorrhizal seedlings also retarded denudation. This was linked to biofilm formation on mineral surfaces in both treatments. These findings support the idea that biofilm not only accelerates the weathering process, but also regulates denudation losses by acting as an inhibiting layer around the mycorrhizosphere and rhizosphere. |
