Scale matters? Exploring the effect of scale on fungal–mineral interactions

Oxalate is considered to be an important fungal weathering agent, but measured bulk soil concentrations in boreal forest soils are too low to expect a significant effect on mineral dissolution. On the other hand, it is expected that oxalate is heterogeneously distributed in the soil, with localized higher concentrations. Here, a model is presented to explore the effects of an oxalate distribution on feldspar dissolution dynamics. First, fungal distribution was studied in a boreal podzol, using fluorescent techniques. Fungi selectively colonized specific mineral species in the soil, with fungal cover on plagioclase > K-feldspar > quartz. Based on the modelling results, oxalate will not have any major effect on feldspar weathering, unless oxalate stays within a few microns of the surface. The results can be extrapolated to other fungal weathering agents, including protons